Engadget Primed: digital audio basics

| August 8, 2012 | 0 Comments

Primed goes in-profundity on the technobabble you hear on Engadget every day — we dig deep into each topic’s history and by what means it benefits our lives. You be possible to follow the series here. Looking to put in mind of a piece of technology for us to bankrupt down? Drop us a line at primed *at* engadget *dawt* com.

Digital audio. There’s a same good chance that you’ve enjoyed some today. It’s one of the to a greater degree universal aspects of technology. In incident, perhaps the more relevant question would have existence, when was the last time you listened to some analog format? The truth, for various, will be quite some time gone — vinyl purists and the odd cassette frenzied zealot aside. Yet, despite its ubiquity, there’s a lot of misunderstanding and destruction about digital audio. Some believe it’ll none match analog for true fidelity, some assert quite the opposite. Many mourn the lack of a tactile format, in which case others love the portability that comes by zeros and ones.

In this installment of Primed, we take a have an air at the history of digital deep, as well as provide an proem to some of its key components, by the view to helping us penetrate it better. Wondering what bitrate to encode your MP3s at? Or whether you should single out a 96 or 44.1KHz pattern rate? We thought as much. By the time we’re through, these questions should nay longer lay heavy on your contemplation, and you can enjoy that latest Knife Party, or Britney road as much as its bit astuteness allows. What’s bit depth you tell? Well, read on to find out…

Table of Contents

A short-lived history
Digital audio bit by byte
Sample degree
Bit depth
Bit rate
Digital to analog (and iniquity versa)
File formats
Myths, lies and put down acoustics

A brief history

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Before we unravel the digital audio incident, it helps to define exactly what digital audio is. In this impression of Primed we’re looking at the most common method for digitizing audio – Pulse-digest modulation (PCM). While this isn’t the barely way (Sony, for example, developed “Direct Stream Digital” / DSD in quest of the Super Audio CD format), it’s through . far the most prevalent. Likewise, it seems logical to also define what digital audio isn’t — and that would have existence sound converted into, and remaining, electrical signals that be at variance over time, also known as garden class “analog audio.”

Pulse-code modulation is weakly a way of representing the analog electrical notable, in digital form. The signal is “sampled” at steady intervals, and in turn converted to a digital set store by. This is not to be confused with musical sampling, where snippets are recorded toward composition and manipulation. In this sheathe, it refers to taking a order of tiny snapshots of the analog audio to be converted into a digital number. If the signal falls somewhere between integers, it’s rounded up or from a high to a low position to the nearest one (known like quantization). The result is that the eccentric, undulating form of the analog audio is shivered down into a series of uncommon samples, one after the other. In numerous company ways this is analogous to a flip-main division , where a collection of stills, while played (or “flipped”) in quick chain, created a fluid moving image. We’ll case into these component parts, and yonder, over the course of the count, but for now, this simple relation will help us understand the basic universal.

While it’s always hard to make fast down the exact origins of one idea — especially one like pulse-digest modulation, where a number of parties were involved — sifting out the plentiful and significant contributions from the gold pan of relation tends to bring up the identical names time and again. When it comes to digital audio, undivided such large-nugget name is Harry Nyquist. Working in quest of Bell Laboratories, Nyquist (among other things) place out theories regarding telegraph speed and transmittance that would pave the way in quest of future digital audio developments. His operate in this area would outline various of the fundamental principles required as being digital communications, especially in regard to required illustration rates and bandwidth limitations, and build upon previous ideas, like Time Division Multiplexing and seasonable facsimile machines.

Some years later, Claude Shannon (too of Bell Labs) would consolidate crowd of the prevailing ideas on the subject in his 1948 bills of exchange “A Mathematical Theory of Communication” that would reference the work of Nyquist significantly. Shannon would besides contribute to the further development of beating-code modulation (along with Bell alumni Bernard M Oliver and John R Pierce) at on every side the same time, using technology that eliminated more of the issues (such as tangle circuitry) from the earlier, but conceptually uniform, implementation from Briton Alec Reeves in 1938.

With the cornerstone ideas in set, digital audio would start to slowly excite from the realms of telecoms out into the broader collegiate and commercial fields. In terms of digital recording, according to the Association during the term of Recorded Sound Collections, Nippon Columbia from Japan (moreover known as Denon) would pioneer its application in the late ’60s and forward ’70s, releasing the first commercial digital recording: the LP “Something” through . Steve Marcus. Other pushes in the erect direction would come from American Thomas Stockham, who would push zealous 16-bit recording in the US. It’s not to the time when the start of the ’80s, which time Philips (after working with Sony) demonstrated the sort of would be the standard Compact Disc — eventually going into production in 1982 — that digital would actually turn a corner and gain traction. More formats would follow, including DAT, MINI-disc and DCC, on the other hand no physical medium would ever sincerely topple the ubiquitous CD. Of direction, we all know the next chapter. MP3 (and other) toothed formats would combine with increasingly affordable home computers to gently, on the contrary definitively, chip away at the CD’s exclusive possession, bringing us to the present time. CDs are still around of run, but as a diminishing stock of vestige shops around the globe will attest, the MP3 is the of the present day king.

Digital audio bit by byte

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Now that we know more hither and thither the background, it’s time to earn out the scalpel, and start dissecting. What makes it click? What are the key factors in articles of agreement of quality? What do all the unlike numbers mean? We’ll let’s hop right in and find out.

Sample Rate

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If you remember, earlier on we compared PCM to a flip-main division . Well, in this analogy, sample charge would be the number of pages through second. A one-page-per-secondary flip-book won’t show you a great deal of detail, whereas one with a 1,000 pages per second will bring it to you through much more fluid fidelity. This, still, is a somewhat simplistic metaphor. The example rate also has a bearing forward the top audio frequency that have power to be reproduced. That’s to saw, the higher the sample rate, the higher the oftenness range that can be recorded. The scale sample rate for commercial CDs is 44,100 state of things per second, or 44.1KHz, acknowledgments in no small part to the bandwidth limitations of NTSC VCRs, that were used as early digital tape recorders. The theoretical highest frequency that can be recorded is in truth. half of the sample rate, to such a degree in the case of the CD, that’s 22,050 Hz (or 22KHz). As in the greatest degree human hearing can typically — at good in the highest degree — hear between 12Hz – 20KHz (bestow or take) this arguably makes 44.1KHz rich for our general consumption (though some like to debate the merits of higher pattern rates). By contrast, if you were to decrease the sample rate to, for model, 10KHz, the maximum frequency you could snatch would be 5KHz, which would exist notably “duller” with a lot of the outgo-end / higher-pitched sounds removed.

Bit Depth

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Bits, digital data has them, and their reference to practice in relation to audio is similar to that of imaging. Remember those crunchy-looking images from the forward internet? That’s a direct event of low bit depth. If scantling rate is the number of “slices” from one side to the other time, bit depth could be considered the reckon of levels, or vertical increments, to be turned to account to each sample. A higher scrap depth means more distinct numerical values to exhibit the signal / voltage. With more values, the adapt of quantization, or rounding up and the floor, is decreased. This means the suit of noise introduced is lower. The CD vexillum has a bit depth of 16 bits, what one. offers 65,536 discrete values, though 24 bits will bring this contain up to well over 16 the masses.

DNP Primed Digital Audio basics

A lower bit depth image

Bit rank

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Not to have existence confused with bit depth, bit reprimand simply outlines the total amount of data used every second. Again, using the CD type, which has a bit depth of 16 and a example rate of 44.1KHz, the mite rate is the result of multiplying these two song. So, 16 x 44,100 = 705,600 bits per second for a mono recording, or 1,411.2Kbps toward stereo. Our friend, the MP3, be able to be encoded with a maximum bit rate of 320kbps (more on this later) and in this box the rate refers to compressed bits, and subsequently the brevity ratio. Bit rate can also have existence used to work out the sizing of an audio file if you apprehend how long it is. For illustration, a 320kbps MP3 has 320,000 bits of given conditions a second, which is 40KBps (report the capital B for Bytes). A five-diminutive MP3 has 300 seconds, which would average 300 x 40KB, to give us a 12,000KB (aka 12MB) file. This is applicable when the mite rate is fixed, but you may moreover have heard of variable bit tax, or VBR, which — as the repute suggests — varies the bit rate used with the aim of having smaller files, with minimal impact on overall quality (through . lowering the bit rate when there are low frequency sounds, or put to rest etc.).

Digital to analog (and laxity versa)

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Okay, in such a manner this Primed is about digital audio, wherefore then are we looking at converting it back to analog afresh? Well, simply put, you might score a song entirely with software, and carry out it in a digital format, however we’re guessing you’ll eventually be destitute of to listen to it? While technology is advancing, we humans are largely analog devices, and thus to hear the actual sound, it indispensably to be converted back at some point, to make those speakers or headphones vacillate sweet, sweet musical air on to our ear drums – and this is to which place the digital-to-analog converter (DAC) comes in. We’ve even now covered what these actually do steady a technical level above, but it’s of importance to remember their existence. By converting those 16- or 24-mouthful samples back into voltage, we procure sound, and the process goes the couple ways (i.e. when recording from a microphone). Most computer soundly cards will do both (A to D and D to A,) and in the greater number of cases you won’t lack to worry too much about it. At minutest now, when you’re reading the back of the box during the term of a swanky new audio interface, and it says A/D and D/A conversion at 24-bit / 192KHz, you should comprehend what that means.

File Formats

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So you have your newfound apprehension for how audio goes digital, yet what about all those file formats? WAV, MP3, AAC, FLAC? Why in such a manner many? Good question, and one that’s not unconstrained to answer. What we can act , however, is look at some of the in greater numbers popular ones and understand their individual advantages (and drawbacks).

WAV / Wave

The WAV or Wave toothed is one of the most public uncompressed formats. Originally a Windows format, it’s from that time become extremely widely supported be it Linux, OS X, or any mobile platform and beyond. The capital advantage beyond versatility is that it’s a “lossless” format, sense audio is typically uncompressed, and is to a high degree similar, though not identical to, CD audio. The downside to this, of route, is that file sizes tend to be large. Using the calculations mentioned in the heavenly heights, a five-minute audio file recorded at 16-piece, 44.1KHz would create a 53MB toothed.

AIFF

Short for Audio Interchange File Format, AIFF is similar to WAV in that it is uncompressed and lossless. Whereas WAV started attached Windows, AIFF found favor with the Macintosh platform, by its origins in the Interchange File Format from Electronic Arts. AIFF likewise stored integers in the arguably other thing efficient big-endian format which was moreover the default on Macs and Linux, if it be not that ultimately lost out to WAV, thanks to the popularity of Windows. Again, like WAV, help is wide, and file sizes are capacious. There is also an AIFF-C / AIFC variant which is “lossy” / compressed.

MP3

MP3s, you be obliged them. We’re pretty sure you’re apprised of what these are. A compressed, or “lossy” format developed by the Moving Picture Experts Group. Clever algorithms keep fidelity, while reducing file sizes, through . compressing the data which is believed to exist hard to hear in its primordial form. When encoded at a grain rate of 128Kbps, the resulting toothed will be approximately 1/11th the greatness of the uncompressed original. This ratio obviously changes when a different duty is employed. For example the greatest bit rate of an MP3 is 320Kbps which is a much more favorable pinching ratio nearer to 4:1. Should you wish to be sure more about the origins of the omnipresent specification, there are lots more minutiae about the MPEG-1 and MPEG-2 stratum III standards online, which make choice restroom reading, but are beyond the vent of this article. The positives of the MP3 format are well-known — feeble file sizes with minimal impact to audible nobility. As such, it has been adopted during the time that the standard format for many media players and devices. The downsides are that, no matter how good the final product is, you are losing some data on the way, which for purists and audiophiles isn’t visionary. Many arguments have been had respecting the noticeable differences between a dear-bit-rate MP3 and a WAV file which, to date, have never been precisely settled, and likely never will.

AAC

If you’ve for aye used iTunes, then there’s a virtue chance you’ve met the AAC. Apple’s preferred compressed format is compose default encoding / compression choice in its omnipresent software. The AAC format was hoped to exist the successor to MP3, as it offers equipollent quality with a lower bit defame (this can depend on the encoder, of line of progress) but as is often the inflection, the general public can have other ideas. While the format is widely supported transversely a variety of platforms, it in no degree quite received the hardware, and user, espousal of the MP3, despite some sinless technical improvements, such as support toward high sample rates (96KHz compared to MP3′s 48KHz max).

FLAC and across

So far the benefits of single format have been almost directly proportional to their drawbacks, i.e. a descry-saw with audio quality on human being end, and file size on the other. The Free Lossless Audio Codec tries to take attached both of these qualities (high truth and smaller file sizes) and squeeze them into the similar pot. It does so with some success, with the official site since the standard claiming an average pithiness of 53 percent in tests. As FLAC is undissembling source, and therefore non-proprietary, it has gained wider carry on than some of the competing lossless formats like as Apple Lossless and WavPack. This comparison of abilities has also earned FLAC a dedicated following, nevertheless file sizes are still larger than those offered by MP3 and AAC, which can quiescent make these skinnier formats appealing to smaller quantity demanding consumers.

There are, of methodical arrangement, many more digital formats, such viewed like WMA, OGG (Vorbis), MP2 and in like manner on. To exhaustively list them in the present state would require a few more pages, or possibly a Primed of its own. The sheer distinction, however, is whether they are lossless or not, and in that case whether compression is involved. While abet for some is greater than others, widely available and popular software media players be possible to usually support all of them natively, or if not, then at least by swelling with downloadable codec packs.

Myths, lies and doom to perdition acoustics

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Knowing what makes up an audio file is merely part of the story, there are absolutely a swathe of other contributing factors that be possible to have a bearing on the legal. First of all, your ears. Sadly these aren’t digital, and be able to decrease in reliability over time. Secondly, there’s the audio itself. Digital determine only reproduce what you feed into it in the foremost place. If the recording is dishonest, poorly mixed, or taken from some inferior source, it will only subsist as good as the weakest bond in the chain. So, theoretically, a 128Kbps MP3 toothed could be better quality than a WAV toothed, if some of the above factors modify one, and not the other. Another resolved mode of action of thinking of it is that you puissance convert an MP3 to a WAV, still it won’t gain anything in the operation (other than extra file size). That said, it’s an interesting test to exercise on that friend who swears they can tell the difference. Only when two files are from the same fountain-head. well are these issues relevant. It may present the appearance obvious, but the temptation can be to fixate on the pure fourth book of the pentateuch; census of the hebrews and not some of the equally essential external factors.

Go on to any audio forum, and it won’t take lengthy before you find a thread from one place to another which format is the best, or whether you be possible to hear the compression in MP3s and such on. In fact, don’t till doomsday do that, unless you want to interpret pages and pages of heated debate between parties solidly determined of the others’ error. Each format has its merits, and the greatest part important factor (particularly where music is concerned) is that it sounds kind to you, and that you have the advantage it. However, knowing that low tittle depth or sample rates can take pleasure in your end result, will arm you by the tools to get the greatest in quantity out of your audio next time you’re encoding it.

[Image credit: IEEE History Center]
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