Speaker 1: Get in touch with technology with tech Stuff from half
Speaker 1: stuff works dot com. Hey everybody, it's Jonathan Strickland here
Speaker 1: with text Stuff classic episodes. We're doing some Saturday morning
Speaker 1: reruns for you guys. This is a special series where
Speaker 1: we're going to dig up some classic episodes of tech
Speaker 1: Stuff and present them to you guys who may not
Speaker 1: have had a chance to listen to them, especially if
Speaker 1: you're a brand new listener. First of all, welcome. If
Speaker 1: that's the case, I hope you enjoy these episodes. This
Speaker 1: one is called The Dirt on Digital Audio, and it
Speaker 1: is an episode all about the actual technical process of
Speaker 1: recording audio into a digital format and what that requires
Speaker 1: because it's very different from the analog style. I hope
Speaker 1: you guys enjoy it. This episode was originally published on
Speaker 1: November twenty three, two thousand sixteen. And just in case
Speaker 1: you're listening to this one in the far future, I'm
Speaker 1: recording this in two thousand eighteen, So we're gonna time
Speaker 1: travel a bit and listen to this classic episode The
Speaker 1: Dirt on Digital Audio. So to start it all off,
Speaker 1: we all have to take a quick trip to Germany,
Speaker 1: So anyone who is not in Germany get your passport.
Speaker 1: I was actually in Germany not that long ago. I
Speaker 1: got to visit Berlin and had a wonderful time. And
Speaker 1: in Germany there's a company called frown Hofer Gazelle Shaft.
Speaker 1: And you might wonder, well, what does this company do
Speaker 1: they think? I joke that my profession, that my title
Speaker 1: that I should put on my business card it should
Speaker 1: say professional smart person. Well, no joke, that's what these
Speaker 1: people are. They specialize in research and development, applied research.
Speaker 1: It's a whole company that specializes and applied research. And
Speaker 1: it's huge. It encompasses sixties seven institutes and research units
Speaker 1: across Germany. Well back in the eighties and there was
Speaker 1: a researcher named Karl Heinz Brandenburg, and Karl Heinz made
Speaker 1: a breakthrough round uh and came up with this clever
Speaker 1: idea about encoding audio. He was actually working towards creating
Speaker 1: a way that would allow for high audio quality transfer
Speaker 1: but having a low bit rate sampling, so that file
Speaker 1: sizes and transfer times wouldn't get out of control. Because
Speaker 1: you got to remember, this is the eighties, this is
Speaker 1: before the World Wide Web was a thing that would
Speaker 1: that wouldn't happen until the early nineties, so the Internet
Speaker 1: was very young. In fact, they weren't even looking at
Speaker 1: the Internet as a method of distribution for this particular
Speaker 1: type of encoded audio. They were looking at using this
Speaker 1: to transmit across telephone lines. So they needed to have
Speaker 1: something that was going to be high quality but low space.
Speaker 1: So what the heck does that mean? All right? Well,
Speaker 1: digital audio and analog audio are very different things. So
Speaker 1: to understand that, we need to look at how sound
Speaker 1: works and how we describe sound, because that informs how
Speaker 1: we can capture sound and replicate those qualities digitally. So
Speaker 1: stick with me. We're gonna go back to school for
Speaker 1: some basic sound science. And this goes back to the
Speaker 1: way sound physically moves through a medium, whether that's a
Speaker 1: solid or through the air or through water. Sound is vibration.
Speaker 1: Now we sense this primarily through hearing it or sometimes
Speaker 1: feeling it. If it's the right frequency and the right amplitude.
Speaker 1: We can actually feel sound. Anyone who stood close to,
Speaker 1: say a sub wiffer that was really blasting out bass notes,
Speaker 1: you know what I'm talking about. You can feel it
Speaker 1: pressing against you. Well, sound travels through the air when
Speaker 1: molecules vibrate against each other, and this creates instances of
Speaker 1: increased pressure and decreased pressure at what is a hyper
Speaker 1: local level. We're not talking about weather maps here, We're
Speaker 1: talking about tiny little areas. So this increase in decrease
Speaker 1: in pressure is something that we can sense as sound.
Speaker 1: When those changes in pressure affect a diaphragm, such as
Speaker 1: one that's in a microphone or maybe your ear drum,
Speaker 1: for example, it causes the diaphragm to actually move. So
Speaker 1: increased pressure pushes the diaphragm in and decreased pressure doesn't
Speaker 1: really pull the diaphragm out. I mean, you could say
Speaker 1: it it pulls the diaphragm out, but to be more accurate,
Speaker 1: the diaphragm actually pushes outward because the pressure on the
Speaker 1: outside is lower than the pressure on the inside. But
Speaker 1: you get what I'm saying. The diaphragm begins to to
Speaker 1: flex inward and outward depending upon the amount of pressure
Speaker 1: that it's it's encountering. You can imagine this being kind
Speaker 1: of like a drum drum, not an ear drum, but
Speaker 1: an actual drum and striking it. Uh, that's the same
Speaker 1: sort of thing. So sound is the fluctuations of pressure,
Speaker 1: which we can diagram as a wave or a wave
Speaker 1: length a wave form on an x y axis, So
Speaker 1: the horizontal line that access that represents time that has passed,
Speaker 1: and the vertical axis represents the amplitude or the volume
Speaker 1: of the sound wave. The wave length of the sound
Speaker 1: which is the distance between successive points on a wave,
Speaker 1: such as like the successive crests on a wave. That
Speaker 1: tells you a lot about the frequency. So sound moves
Speaker 1: at a constant rate through a given medium, but it
Speaker 1: moves at different rates through different media. So in other words,
Speaker 1: it moves a different speed through a solid than it
Speaker 1: does through air. If the crests of each sound wave
Speaker 1: are really close together, that's a high frequency sound. More
Speaker 1: waves will pass through an arbitrary point within a second.
Speaker 1: The waves that are spaced further apart, that would be
Speaker 1: a lower frequency sound. Higher frequency sounds have a higher
Speaker 1: pitch than lower frequency sounds. So if you hold a
Speaker 1: single note at a constant frequency, you'll have what is
Speaker 1: called a simple harmonic motion. That means the vibrations are
Speaker 1: moving at a constant rate inward and outward. The cycle
Speaker 1: is constant. A tuning fork is a good example of this.
Speaker 1: So if you hear a clear C note played on
Speaker 1: a musical instrument, that could be a simple harmonic motion.
Speaker 1: It won't be, but it could be. I'll tell you
Speaker 1: why it won't be in a minute. So the frequency
Speaker 1: of vibration doesn't change, and so you would get this
Speaker 1: very clear note as a result, And if you were
Speaker 1: to diagram it, you would have very regular crests and troughs,
Speaker 1: all of the same amplitude and distance from each other.
Speaker 1: The frequency and volume would remain constant, assuming of course,
Speaker 1: that you're not trying to change the frequency or volume. Now,
Speaker 1: this is where I point out most musical instruments don't
Speaker 1: produce a single clear note, even if played expertly. They
Speaker 1: actually create several resonant frequencies. So every physical object resonates
Speaker 1: at several different frequencies. You've probably seen this in various programs.
Speaker 1: MythBusters did one about bridges, the idea being that if
Speaker 1: you were to have a group of people marching on
Speaker 1: a bridge at the bridge's resonant frequency, it could cause
Speaker 1: the bridge to start to vibrate and swing out of control. Well,
Speaker 1: there's a reason for this. You may have also seen
Speaker 1: videos of people singing a certain note and causing a
Speaker 1: crystal glass to shatter. That's because that crystal glass does
Speaker 1: have a resonant frequency, and if you can hit that
Speaker 1: resonant frequency at the right volume, you can cause the
Speaker 1: glass to start to deform, or the crystal in this case,
Speaker 1: to deform to a point where it loses integrity and
Speaker 1: it shatters as a result. Well, the resonation of an
Speaker 1: object is dependent upon lots of different factors, and in fact,
Speaker 1: most stuff will resonate at different frequencies, but at different intensities.
Speaker 1: Like there might be one sweet spot, one specific frequency
Speaker 1: that will have the greatest effect, but other related frequencies
Speaker 1: may also have an effect. It will just be to
Speaker 1: a lesser extent. Well, if you were to pluck a
Speaker 1: guitar string, just you've tuned it to whatever note doesn't matter.
Speaker 1: Let's say it's you tuned it to to G and
Speaker 1: you play the G string on your guitar. The note
Speaker 1: that you will hear really over all others will be
Speaker 1: g that that is going to be the one that
Speaker 1: will sound the loudest, But it will also play resonant
Speaker 1: frequencies at a decreased amplitude. In other words, of decreased
Speaker 1: volume so you still hear the intended note above everything else,
Speaker 1: above all the other resonant frequencies. This is called a
Speaker 1: complex tone, and that collection of frequencies in their amplitudes
Speaker 1: is called the sectrum of sound. You get a full spectrum. Now,
Speaker 1: some of the components of that complex tone will be uh,
Speaker 1: imperceptible to you. You there'll be so quiet that you
Speaker 1: wouldn't really notice them. They might affect the overall quality
Speaker 1: of the sound, but in such a subtle way that
Speaker 1: it may be difficult for you to even put it
Speaker 1: into words. Each of those little components is called a partial.
Speaker 1: So in the example of a guitar string, the partials
Speaker 1: are all integers of the same fundamental frequency, and the
Speaker 1: sound has a harmonic spectrum. But as you get further
Speaker 1: away from that fundamental frequency, the amplitude decreases significantly. So,
Speaker 1: like I said, you get far enough away, they are
Speaker 1: technically there, but they might be imperceptible to you. Now,
Speaker 1: some sounds have frequencies that aren't integers of a fundamental
Speaker 1: frequency and are inharmonic Uh. Certain bells, like if you
Speaker 1: hear a bell ring, you can probably pick out a
Speaker 1: couple of different frequencies. There that are not harmon frequencies.
Speaker 1: These are very complex sounds, and to our perception, if
Speaker 1: it's complex enough, it can seem like there's no single
Speaker 1: discernible pitch. They're like there's no fundamental frequency over all
Speaker 1: the others. If it's complex enough, we call it noise.
Speaker 1: That is the technical term. It is noise. Now, the
Speaker 1: unit we use to measure frequency is the hurts uh
Speaker 1: H E R t Z. Typical human hearing ranges from
Speaker 1: twenty hurts, which means a wave will pass a given
Speaker 1: arbitrary point twenty times within a second, all the way
Speaker 1: up to twenty killer hurts, which means a wave will
Speaker 1: pass a particular point in time twenty thousand times in
Speaker 1: a second, or particular point on your wave form twenty
Speaker 1: thousand times in the second. And most of our sensitivity
Speaker 1: tends to be between one or two killer hurts up
Speaker 1: to four or five killer hurts. That's generally where we
Speaker 1: have human voices, and we've really gotten good at picking
Speaker 1: those out of over everything else. So our sensitivity of
Speaker 1: hearing is really concentrated between one killer hurts and four
Speaker 1: killer hurts or two and five depending upon whom you ask.
Speaker 1: Now we get back over to amplitude, that is referring
Speaker 1: to the height of the wave. It also refers to
Speaker 1: the volume the loudness of something. Amplitude means bigness. So
Speaker 1: how big is the sound, Well, the greater the amplitude,
Speaker 1: the louder it is. And amplitudes can have an enormous
Speaker 1: range and affect how we perceive sounds. So, for example,
Speaker 1: take a really complicated classical piece of music. It's just
Speaker 1: easy to explain it in that term. You might have
Speaker 1: a stretch in that classical piece of music in which
Speaker 1: all the instruments are more or less playing at a
Speaker 1: similar volume, so the sound from each instrument section has
Speaker 1: a similar amplitude. But then there might be one segment
Speaker 1: where an instrument group or maybe even a single soloist
Speaker 1: has an increased amplitude and increased volume. It rises over
Speaker 1: the rest of the orchestra, and that peak of the
Speaker 1: amplitude is called the attack of the sound, and the
Speaker 1: entire range of amplitudes is called the amplitude envelope. Now
Speaker 1: this is important when we get to m P three's
Speaker 1: because the way we perceive these sounds uh that that
Speaker 1: has everything to do with the way the MP three
Speaker 1: was designed. The whole point of the MP three was
Speaker 1: to try and create a small file size to represent
Speaker 1: what we can hear and kind of ignore everything else.
Speaker 1: We'll get to that in a little bit more more time.
Speaker 1: So this is really interesting to me. If you take
Speaker 1: a sound and you double its amplitude, you increase the
Speaker 1: amplitude by twofold, a listener would not necessarily feel that
Speaker 1: the sound is twice as loud. Human hearing is incredibly subjective,
Speaker 1: and typically for most listeners, it would require much more
Speaker 1: than doubling the sounds amplitude for them to feel that
Speaker 1: the sound itself was twice as loud. This perception of
Speaker 1: volume is important when we get to the lossy formats
Speaker 1: for audio files. Now I've given you all this information,
Speaker 1: and I know everyone is probably thinking, you know, I
Speaker 1: learned this in primary school, elementary school. All of this
Speaker 1: is really familiar to me, and you're maybe rolling your
Speaker 1: eyes because it's so basic. But I think it's important
Speaker 1: to have that refresher so that you can understand the
Speaker 1: difference between sound as we experience it and sound as
Speaker 1: the way we encode it digitally and replicate it digitally.
Speaker 1: For one thing, this illustrates how sound in the real
Speaker 1: world is a continuum. It's a continuum both in frequency
Speaker 1: and amplitude. You can have sound changing in frequency very
Speaker 1: smoothly from one pitch to another. You can also have
Speaker 1: sound increase or decrease in amplitude in a very smooth way.
Speaker 1: And it is continuous, it's unbroken. It can have smooth transitions.
Speaker 1: And these qualities provide challenges when we want to describe
Speaker 1: something digitally because at the heart of digital information is
Speaker 1: the bit, the basic unit of information. It is a
Speaker 1: unit of information that only has two states zero or
Speaker 1: one is essentially off or on. When you get down
Speaker 1: to defining information in just two states, then you start
Speaker 1: to look at something that is continuous and you realize
Speaker 1: this is going to be a challenge. How do I
Speaker 1: describe a continuous experience in very discrete amounts of information.
Speaker 1: And that's when we get to the methodology we've developed
Speaker 1: to digitally encode sound. I'm going to get into that
Speaker 1: in just a minute, but before I do that, let's
Speaker 1: take a quick break to thank our sponsor. All right,
Speaker 1: let's get back into it. So we've talked about the
Speaker 1: nature of sound. Analog sound, by the way, tries to
Speaker 1: replicate exactly what we would experience in nature. It tries
Speaker 1: to create this continuous experience, so you get these smooth
Speaker 1: waves of frequencies and amplitudes. And that's why some people
Speaker 1: argue that that analog styles of of sound recordings are
Speaker 1: superior to digital ones. I don't necessarily think they're right,
Speaker 1: but they often feel that way. So something like a
Speaker 1: vinyl album, which is an analog format of digital or sorry,
Speaker 1: an analog format of music storage should say sound storage. Uh,
Speaker 1: they think that that is superior to say a c D,
Speaker 1: which is a digital storage format. Uh. And who's to say.
Speaker 1: I mean, like, if your sense of hearing is incredibly
Speaker 1: well tuned, you might be able to pick up on
Speaker 1: some differences. Or if someone did a really terrible job
Speaker 1: encoding music digitally, then that might reveal itself to you
Speaker 1: as well. Uh. But this is one of those things
Speaker 1: that I think a lot of people feel they can
Speaker 1: tell the difference, but if they would do a double
Speaker 1: blind test, they might be surprised at how difficult it is.
Speaker 1: If things if everything's working the way it should, then
Speaker 1: there shouldn't be a perceptible difference at any rate. Digital
Speaker 1: audio has two really important factors. Sample rate and bit depth,
Speaker 1: or to another extent, bit rate. We'll talk about bit
Speaker 1: rate as well. So the sample rate refers to how
Speaker 1: many times you reference an analog sound to create the
Speaker 1: digital version. So sound, like I said, is uninterrupted in
Speaker 1: the analog world, you've got that that nice wave form.
Speaker 1: In the analog world, that's not how digital world works.
Speaker 1: Digital world, we have to describe that sound in a
Speaker 1: series of discrete snippets of sound. It's probably easiest to
Speaker 1: describe this with an analogy to movies on film. If
Speaker 1: you work with film, like you're creating a movie on film,
Speaker 1: then you know that you're not looking at a real
Speaker 1: moving picture when you see the film played out at
Speaker 1: the cinema. Instead, what you're looking at is a series
Speaker 1: of photographs. If you take a film strip and you
Speaker 1: look at it under a light, you'll see it's one
Speaker 1: after another photograph. It's just a series of pictures. It's
Speaker 1: only when you play them back at the right speed
Speaker 1: and you projected onto a screen that you get the
Speaker 1: illusion of continuous motion. But it's not really continuous. It's
Speaker 1: just this series of photographs played at twenty four frames
Speaker 1: per second in the case of actual film. So that
Speaker 1: ends up being very analogous to the way we encode
Speaker 1: digital audio. You take the analog recording and you take
Speaker 1: snapshots of sound. The more frequently you take those snapshots,
Speaker 1: the higher your sample rates. So in other words, if
Speaker 1: you did one a second, your sample rate would be awful.
Speaker 1: You would have a sample rate of one. But the
Speaker 1: higher the sample rate, the closer your digital representation will
Speaker 1: be to the frequency in the analog sound format. Actually,
Speaker 1: what's really important to remember is that your sample rate
Speaker 1: has to be about twice actually does have to be
Speaker 1: twice what the highest frequency sound is in your recording.
Speaker 1: It has to be because as if it's not, it
Speaker 1: cannot encode that sound accurately. It's kind of interesting and
Speaker 1: you might wonder, how do we take these snapshots in
Speaker 1: the first place. Well, if you're capturing audio, let's say
Speaker 1: we're recording to digital, So we've got a microphone set
Speaker 1: up and we're recording to a digital media storage. Like
Speaker 1: let's just say we're recording straight to someone's hard drive.
Speaker 1: So we're talking into a microphone recording to a hard drive.
Speaker 1: So you're using an analog microphone. Let's say you would
Speaker 1: need an analog to digital converter Now this particular component
Speaker 1: can receive discrete voltages from another device like your microphone.
Speaker 1: So your microphone is converting sound into uh differences in voltage.
Speaker 1: That's essentially how it communicates, so that it can then
Speaker 1: send that to some other element. In this case, it's
Speaker 1: sending it to the the analog to digital converter so
Speaker 1: that it can be stored digitally on your our drive.
Speaker 1: So this analog digital converters references or samples the discrete
Speaker 1: voltage many times every second in order to create a
Speaker 1: digital representation of the analog sound. It converts the voltages
Speaker 1: into numbers and a process called quantization, and we express
Speaker 1: those numbers in bits, So these are zeros and ones.
Speaker 1: When you want to play the digital audio, a digital
Speaker 1: to analog converter does the same process in reverse. So
Speaker 1: it takes this digital information, these zeros and ones and
Speaker 1: converts it into a series of discrete voltages, which then
Speaker 1: can be amplified and sent to a speaker and create sound.
Speaker 1: So all of that's really important. But now let's let's
Speaker 1: talk about some concrete examples, and the best way to
Speaker 1: do this is to go with compact discs. Because we
Speaker 1: have a standard sample rate for compact discs, and that
Speaker 1: standard sample rate is forty four point one la hurts
Speaker 1: to create CD equality audio. That means that the audio
Speaker 1: is sampled forty four thousand, one hundred times every second
Speaker 1: the way they hear you say, the range of human
Speaker 1: hearing you said only goes to twenty hurts to twenty
Speaker 1: killer hurts. If it only goes up to twenty killer hurts,
Speaker 1: why are you sampling at forty four thousand, one hundred
Speaker 1: times every second? If it's twenty thousand times a second
Speaker 1: for the frequency, why go up to four thousand, one
Speaker 1: hundred Is there some relationship between that and the c
Speaker 1: D sample rate? And the answer is yes. So there
Speaker 1: is a theorem called the Nyquist Shannon sampling theorem, and
Speaker 1: that states that the sample rate must be twice the
Speaker 1: maximum frequency of a recording in order to describe the
Speaker 1: frequency properly. So the general thought is the maximum frequency
Speaker 1: most humans can here's twenty killer hurts. And for that reason,
Speaker 1: Phillips and Sony when they were working to create the
Speaker 1: CD format to make it a standard, they decide on
Speaker 1: forty four point one killer hurts as that standard sample
Speaker 1: rate for c D audio. It was more than double
Speaker 1: the top frequency generally considered to be in the upper
Speaker 1: level of human hearing. But what happens if you were
Speaker 1: to lower the sampling rate. What if you didn't sample
Speaker 1: at What if you sampled at let's say sixteen killer hurts,
Speaker 1: so sixteen thousand times a second you sample it well,
Speaker 1: that means you would only be able to record and
Speaker 1: replicate any sound with a frequency up to eight killer
Speaker 1: hurts or less, so eight thousand hurts or less. But
Speaker 1: if you had any sound that was greater than eight
Speaker 1: thousand hurts or eight killer hurts, anything higher than that,
Speaker 1: it would be folded down to fit below the eight
Speaker 1: killer hurts limit. Perceptually, that means the sounds you would
Speaker 1: hear in the playback could include frequencies that were not
Speaker 1: present in the original performance of that sound. So let's
Speaker 1: say that I'm using a sample rate of sixteen uh,
Speaker 1: you know, killer hurts, and someone is playing a musical
Speaker 1: instrument and they play a note that's at a nine
Speaker 1: killer hurts frequency. Well, because I'm sampling at sixteen killer hurts,
Speaker 1: my limit for frequencies is eight killer hurts. If you
Speaker 1: play something at nine killer hurts, what happens is it
Speaker 1: the recording seems to fold the sound back, and it
Speaker 1: folds it back at the same limit that the sound
Speaker 1: goes over, the sample rate rather the Nyquist limit, I
Speaker 1: should say, not the sample rateself, but the Nyquist limit.
Speaker 1: So nine killer hurts sound played, My limit is eight
Speaker 1: killer hurts. Well, nine killer hurts is one killer hurts
Speaker 1: more than eight, so it folds it back and the
Speaker 1: sound you would hear on the recording would be seven
Speaker 1: killer hurts. So the original sound is nine killer hurts.
Speaker 1: The playbacks sound is seven killer hurts, and you would
Speaker 1: hear something recorded that wasn't actually played. That's why you
Speaker 1: have to have a really high sample rate so that
Speaker 1: you don't have these instances where sound gets folded back
Speaker 1: into the frequency range, because otherwise what you were hearing
Speaker 1: is not an accurate representation of what was actually generated
Speaker 1: what you were trying to record. This whole phenomenon, by
Speaker 1: the way, is called fold over or sometimes alias sing.
Speaker 1: So that's sample rate. But then we've got bit depth. Now,
Speaker 1: this is all about measuring the volume or amplitude of
Speaker 1: a sound. So you have a range. You just make
Speaker 1: an arbitrary range to say, like we're gonna go quietest
Speaker 1: to loudest, and you just define what that range is.
Speaker 1: It could literally be any range. Let's say you say
Speaker 1: zero to one. Zero is dead silence, no sound at all.
Speaker 1: One hundred is as loud as the sound ever gets.
Speaker 1: It's the peak volume of sound. That means you can
Speaker 1: describe all the different volumes within that recording at a
Speaker 1: number between zero and one hundred. But let's say you
Speaker 1: take that same recording and instead of making the range
Speaker 1: zero to one hundred, you say it's zero to two thousand.
Speaker 1: You haven't made the volume louder. The volume is still
Speaker 1: the exact same as it was when you called the
Speaker 1: range zero to one hundred. But what you have done
Speaker 1: is added more units. You've created more precise steps between
Speaker 1: absolute silent and as loud as it gets. So you've
Speaker 1: just increased the size of the range so that you
Speaker 1: can be more precise in the differences in volume. And
Speaker 1: this is really important. So let's say that you've got
Speaker 1: a sound that you rank at seventy eight and another
Speaker 1: sound that you rank at seventy nine, and that's gonna
Speaker 1: be the same for both of these changes. Uh, just
Speaker 1: two different examples. Actually, So you've got your zero to
Speaker 1: one range and a seventy eight would be seventy eight
Speaker 1: percent of the loudest sound in the entire recording, and
Speaker 1: at seventy nine would be a seventy nine of the
Speaker 1: loudest sound in the entire recording. That's an actually pretty
Speaker 1: hefty jump. But let's say we instead went with that
Speaker 1: zero to two thousand range and you still had seventy
Speaker 1: eight and seventy nine. Well, seventy eight would represent three
Speaker 1: point nine percent of the full volume and seventy nine
Speaker 1: would represent represent three point nine five of a full volume.
Speaker 1: In other words, you'd be able to mark much more
Speaker 1: subtle differences in volume, and that means you can have
Speaker 1: more nuance in your recording. And since we're talking about
Speaker 1: a natural sound to start off with, so you're taking
Speaker 1: a natural sound and you're trying to digitize it. Smooth
Speaker 1: changes in amplitude are possible in natural sound. Using a
Speaker 1: broader range to describe the volume is best if you
Speaker 1: want to get an accurate representation or resolution of that sound.
Speaker 1: Going back to that zero to one range changes in
Speaker 1: volume would be more chunky. Two sounds that have slight
Speaker 1: differences in amplitude would end up being defined as being
Speaker 1: identical because you wouldn't have the precision. You know, you
Speaker 1: couldn't say this one seventy eight and a half. It
Speaker 1: would either be seventy eight or seventy nine. So you
Speaker 1: could have two sounds that in greater precision you could
Speaker 1: tell the difference between their volumes. But if you have
Speaker 1: that lower, that more shallow bit depth, you wouldn't be
Speaker 1: able to tell the difference of it. You would lose
Speaker 1: that nuance, that subtlety. This is part of the reason
Speaker 1: why people say, like a lot of the modern music
Speaker 1: has uh lower ranges and changes in volume, like the
Speaker 1: the loudest loud parts and the softest soft parts. That
Speaker 1: range has decreased over time, which a lot of people
Speaker 1: have argued has meant that music has gotten less complex
Speaker 1: and therefore, in some minds, less interesting. That's on a
Speaker 1: related uh kind of philosophy to what I'm talking about here.
Speaker 1: So you want to have those smaller steps between each
Speaker 1: unit so you can create greater resolution, more smoothness to
Speaker 1: the recorded audio. And it's actually the bit rate and
Speaker 1: CD audio that will help make the sound seem smooth.
Speaker 1: So if you ever listened to eight bit music, you know,
Speaker 1: like the kind from old video game consoles. That sound
Speaker 1: is really harsh and sort of chunky. It has an appeal,
Speaker 1: but it's not you know, it's not smooth at all.
Speaker 1: It can create an amazing effect, but if you want
Speaker 1: to represent true analog sound, it's not awesome. But if
Speaker 1: you went up to sixteen bit, that's CD quality bit depth,
Speaker 1: it's much better. Uh, professional recording studios will do twenty
Speaker 1: four bit or thirty two bit because they're gonna do
Speaker 1: a lot of post processing work on those audio files.
Speaker 1: And when you do that post processing work, if you
Speaker 1: do it at sixteen bit, the stuff you're doing, the
Speaker 1: changes you make, can become noticeable, and most times you
Speaker 1: don't want that. You don't want it to be you know,
Speaker 1: you don't want it to stand out from the rest
Speaker 1: of the audio file. But that's the only reason they
Speaker 1: go up to twenty four bit or thirty two bit.
Speaker 1: There'd be no point in playing it back at that rate,
Speaker 1: that bit depth, because human hearing is not so adept
Speaker 1: to tell the difference, at least not for most humans.
Speaker 1: So if you played back a recording at sixteen bit
Speaker 1: and another one at twenty four bit, and it's the
Speaker 1: same piece, most people would not be able to tell
Speaker 1: the difference because you've already reached a resolution that equals
Speaker 1: the precision of human hearing. Keeping in mind again, human
Speaker 1: hearing is subject. If not everyone is equal, there's some
Speaker 1: people who have incredible hearing who may be able to
Speaker 1: pick out that difference. I am not one of those people,
Speaker 1: but I am a person who's going to tell you.
Speaker 1: We'll get to the last section in just a bit,
Speaker 1: but first let's take another quick break to thank our sponsor.
Speaker 1: All Right, so bids depth. What we just talked about
Speaker 1: that can be thought of is how well the sound
Speaker 1: is described, and the sampling rate is how frequently or
Speaker 1: how much the sound is described. And CD Audio quality
Speaker 1: has sixteen bit audio. That means that they actually have
Speaker 1: sixty five thousand, five hundred thirty six different levels of
Speaker 1: volume that they can describe within an audio track. So
Speaker 1: my example of zero to two thousand that is primitive
Speaker 1: compared at the c D audio because it has the
Speaker 1: sixteen bit style six five hundred thirty six different levels.
Speaker 1: And how is that possible? Well, when we say sixteen bit,
Speaker 1: remember a bit represents two states zero or one. So
Speaker 1: you take the number two and then you raise it
Speaker 1: to the power of sixteen. Uh, so you multiply to
Speaker 1: by itself sixteen times and you get sixty five thousand,
Speaker 1: three D fifty six. So that's that's where that number
Speaker 1: comes from. Now, with your digital sample, you have a
Speaker 1: collection of points that roughly replicate the shape of an
Speaker 1: analog sound wave. It's gonna look a little funky, but
Speaker 1: you'll be able to see what the frequency and amplitude
Speaker 1: generally was of the original recording if you were to
Speaker 1: plot this on an X y axis. But if you
Speaker 1: were just to connect each successive point with a straight line,
Speaker 1: even as close together as they would be, because you're
Speaker 1: looking at forty four thousand one times a second, it
Speaker 1: had sound pretty awful. So we actually use an algorithm
Speaker 1: called interpolation to join the points smoothly to imitate a
Speaker 1: sound wave form, and that gives a musical playback program
Speaker 1: the ability to replicate an analog wave form. And that's
Speaker 1: actually called pulse code modulation or pc M. And if
Speaker 1: you store audio uh intact this way, you would have
Speaker 1: what we call a lossless audio file, which means exactly
Speaker 1: what it sounds like. None of that data would ever
Speaker 1: get filtered out of the file, even if the sounds
Speaker 1: were beyond the range of human hearing, they would be
Speaker 1: recorded and you would have a lossless file format. Those
Speaker 1: files tend to be quite big, depending upon how long
Speaker 1: a recording you make, of course. All right, so now
Speaker 1: here's where it gets a little confusing. And I think
Speaker 1: I even said bit rate a couple of times when
Speaker 1: I really meant bit depths earlier. But up to this point,
Speaker 1: I really was talking at depth. So my apologies to
Speaker 1: all of you out there if a bit rate slipped through,
Speaker 1: because I did not mean it. Now I'm going to
Speaker 1: talk about bit rate and show you how it's different
Speaker 1: than bit depth. Bit Rate refers to the amount of
Speaker 1: data audio uses per second or requires per second of recording,
Speaker 1: and you derive bit rate from the bit depth and
Speaker 1: the sampling rate. It's represented as bits per second. So again,
Speaker 1: let's go to ceed equality sound. That makes it easy.
Speaker 1: You have thousand one samples per second. You've got sixteen
Speaker 1: bits or two bites, because remember a bite is eight bits,
Speaker 1: so you've got two bites to describe each sample. So
Speaker 1: two bites for one samples per second. Uh plus you
Speaker 1: probably are gonna have to multiply that by two because
Speaker 1: you're probably recording in stereo, so you have to do
Speaker 1: that once reach track, so you get that number, then
Speaker 1: you have to multiply that by sixty seconds to determine
Speaker 1: how much data per minute you are creating when you're recording,
Speaker 1: and with seed quality audio, that ends up being about
Speaker 1: ten megabytes of data per minute. Now these days that's
Speaker 1: not really that big a deal because we're dealing with
Speaker 1: super fast internet speeds and enormous hard drives. But just
Speaker 1: a few years ago, that was considered to be a
Speaker 1: really sizeable file, I mean an enormous file, and so
Speaker 1: if you wanted to find a way to distribute digital
Speaker 1: audio so it didn't take up too much space, you
Speaker 1: had to figure out how you could compress those files
Speaker 1: and make them smaller, make them more manageable. And now
Speaker 1: we can finally get back to Germany and Hair Brandenburg.
Speaker 1: You thought we left him behind, We didn't. He was
Speaker 1: just part of a flashback. So let's go to the
Speaker 1: MP three. First of all, it gets his name from
Speaker 1: the Motion Picture at Spurts Group, also known as IMPEG.
Speaker 1: It was part of a project that IMPEG was doing
Speaker 1: that was looking at ways of compressing audio. Along with
Speaker 1: the work that they were doing with video files. It's
Speaker 1: actually named after the process that they developed, called IMPEG
Speaker 1: Audio Layer three. So yes, there was a layer one
Speaker 1: and a layer two. Layer three was a refinement of
Speaker 1: the approach and was the one that was actually successful
Speaker 1: in the market. Now, Brandenburg was working with an instructor
Speaker 1: he was pursuing Brandenburg was pursuing a PhD at the
Speaker 1: time and trying to come up with a practical means
Speaker 1: of transmitting digital audio across phone lines, and in the
Speaker 1: process he began to experiment with algorithms that could take
Speaker 1: digital audio information and determine which bits are significant. Anything
Speaker 1: that was deemed insignificant could be discarded. So the thinking
Speaker 1: was that information we cannot perceive as human beings is worthless.
Speaker 1: There's no point in preserving it in an audio file format.
Speaker 1: It's just taking up space that we can't even perceive
Speaker 1: when we play it back, So there's no reason to
Speaker 1: replicate it, there's no reason to record it. Leave it out,
Speaker 1: and that way you could compress digital audio files. Or
Speaker 1: to put it another way, if the algorithm determined that
Speaker 1: a sound was outside the range of human hearing, it
Speaker 1: would drop it from the encoding process, so you get
Speaker 1: a sound file much smaller than the more accurate representative version.
Speaker 1: So the lossless version would be more accurate to the
Speaker 1: original sound. But this new version, what we would call
Speaker 1: a lossy version, a compressed file, would be able to
Speaker 1: replicate it pretty well if it's designed properly, and maybe
Speaker 1: to a point if you design it well enough that
Speaker 1: you couldn't tell the difference between the two. Uh. That
Speaker 1: took some time. That was not easy to do. So
Speaker 1: the new file, the new version, the compressed one, the
Speaker 1: lossy format, would only have the actual relevant data, and
Speaker 1: from that point forward, the challenge was to determine what
Speaker 1: are the benchmarks to figure out what is relevant versus
Speaker 1: what is irrelevant, Because if you lose too much information,
Speaker 1: you change the quality of the recording, meaning it's no
Speaker 1: longer an accurate representation of the original sound. So you
Speaker 1: might say that any sound below twenty hurts isn't relevant
Speaker 1: because it's below the range of your typical human humans
Speaker 1: ability to hear. You might say that anything above twenty
Speaker 1: thousand hurts or twenty killer hurts is irrelevant because humans
Speaker 1: typically can't hear sounds above that frequency. You might say
Speaker 1: that sounds at a certain amplitude or lower are irrelevant
Speaker 1: because they're so quiet that humans wouldn't hear them. Or
Speaker 1: you might say that if a certain sound is at
Speaker 1: a lower amplitude and a different sound is at a
Speaker 1: higher amplitude, the higher amplitude sound is drowning out the
Speaker 1: lower amplitude sound, and so we humans don't really perceive
Speaker 1: the lower amplitude sound. This is where we get into psychoacoustics.
Speaker 1: It's not just what we hear, but how we perceive
Speaker 1: the sound itself. And a lot of that went into
Speaker 1: formulating the algorithms to figure out how to compress this
Speaker 1: music in a way where you get a recording that
Speaker 1: represents the original without you know, compromising too much and
Speaker 1: still getting the file size to a manageable size. And
Speaker 1: these are the decisions you have to make to figure
Speaker 1: out which bits of information you keep in which ones
Speaker 1: you ditch. Brandenburg and a team we're working on refining
Speaker 1: this approach in the late eighties and early nineties, And
Speaker 1: he said, at one point he thought he had nailed it,
Speaker 1: and then he heard an acapella song. It was Tom's
Speaker 1: Diner by Suzanne Vega, And then he listened to the
Speaker 1: compressed MP three version of that song using the the
Speaker 1: version of MP three that had been developed up to
Speaker 1: that point, and he said, it ruined the song. It
Speaker 1: trashed it. It sounded terrible. He said that other representations
Speaker 1: of music seemed fine with this particular approach, but when
Speaker 1: they went with this stripped down acapella song with this
Speaker 1: particular kind of you're in the middle of a space
Speaker 1: listening to Suzanne Vegas sing, it ruined her voice. And
Speaker 1: so the team began to tweet the compression algorithms to
Speaker 1: correct for this problem, and it took a lot of
Speaker 1: work to figure out, Okay, well, what are the elements
Speaker 1: of sound that we messed with that have created this issue,
Speaker 1: and ultimately they were finally able to create an MP
Speaker 1: three file that didn't distort or ruin the recording. Brandberg
Speaker 1: said he listened to that song somewhere between five hundred
Speaker 1: and a thousand times, and then he saw Suzanne Vega
Speaker 1: performance live and he was able to recognize all of
Speaker 1: those subtle changes in her voice because he had paid
Speaker 1: so close attention to it during the process of tweaking
Speaker 1: this algorithm. He said, ultimately, the real telling thing is
Speaker 1: he still enjoyed the song, which says a lot about him. Me.
Speaker 1: I can't stand that song, but maybe it's just because
Speaker 1: to me there's a point where it just sounds like
Speaker 1: someone is just singing about what they're doing. And I
Speaker 1: do that every day. No one gave me a record deal, alright.
Speaker 1: So getting back to MP three, they had finalized the
Speaker 1: foul format and created the standard, but it was just
Speaker 1: one of several possibilities for encoding audio and it didn't
Speaker 1: immediately take off. It wasn't immediately adopted by consumers. The
Speaker 1: team had identified the Internet as a possible distribute distribution
Speaker 1: method for MP three files, rather than just over telephone lines.
Speaker 1: They said, well, can technically we could send and B
Speaker 1: three's across the Internet, so you could send manageable sized
Speaker 1: files across this network. Until life fourteen, they created the
Speaker 1: file extension DOT MP three. Now it would take a
Speaker 1: little bit longer for software to take advantage of this.
Speaker 1: One of the early programs was win amp, which made
Speaker 1: MP three decoding accessible, and from that point the file
Speaker 1: format began to take off. To follow would be dedicated
Speaker 1: MP three players and sites that allowed people to upload
Speaker 1: and download compressed audio files, which also indicated a rise
Speaker 1: in piracy, and then in response to the rise in piracy.
Speaker 1: We saw an increase in d r M strategies digital
Speaker 1: rights management or copy protection if you prefer, and that
Speaker 1: all really ended up shaping a lot of the policies
Speaker 1: and strategies that affect the Internet today. So you could
Speaker 1: say that the MP three is one of the reasons
Speaker 1: why the Internet is the way it is right now,
Speaker 1: and why arguments both for and against net neutrality have
Speaker 1: formula aided in certain ways. A lot of it is
Speaker 1: shaped by the MP three. So that kind of wraps
Speaker 1: up this discussion about digital audio in general and a
Speaker 1: little bit on MP three files. In the next episode
Speaker 1: of this series, I will dive into a more technical
Speaker 1: explanation of what is actually going on with the MP
Speaker 1: three compression algorithms, and I bet you can't wait to
Speaker 1: learn all about fast Furrier transforms. I know I can't,
Speaker 1: And like I said, I have other episodes to sprinkle
Speaker 1: in between this one and the next one and then
Speaker 1: the third one, so that way you won't just get
Speaker 1: digital audio overload. And if you guys have any comments
Speaker 1: or questions or suggestions for show topics or people I
Speaker 1: should interview, or maybe people I should have on as
Speaker 1: a guest host shoot him my way. My email is
Speaker 1: tech stuff at how stuff works dot com, or you
Speaker 1: can always drop me a line on Facebook or Twitter
Speaker 1: with the handle tech stuff hs W and I'll talk
Speaker 1: to you guys again really soon. For more on this
Speaker 1: and thousands of other topics, is it how stuff works
Speaker 1: dot com