The Beat Patrol

Max Mobley – “Dithering Away the Compact Disc” (2009)

April 27, 2009 at 11:16 am (Music, Reviews & Articles)

Recent article (March 30, 2009) on the (resurrected) Crawdaddy! website about the coming death of the compact disc. Considering I probably own about 7,000 of the damn things (give or take a few thousand), I really hope CDs don’t completely die out. Even though I’m all for downloading as much as the next person, there are simply thousands of albums that I could not live without the physical product.  It makes me wonder if in the future, nobody will be recording albums anymore. Or if they will just be digital “albums” – but that just doesn’t replace the beauty of a product with liner notes and printed lyrics and what have you… 
The compact disc is dead! Long live the compact disc! 

I read the news today oh, boy—the compact disc had just lost the war. A crowd of people stayed away. And now we’re stuck with fucking downloads. Stupid, crap-sounding, immediately gratifying but ultimately dissatisfying downloads. They deprive as much as they empower. Goodbye, context.

From a greedy capitalist point of view, this news makes sense. For the disposable background rock enthusiast, this news was probably met with a yawn. But for the rock album fan, the news is rather sad. And for the musician earning a living from his art = pain, why, I wouldn’t be surprised if he blew his mind out in a car—with his demo still spinning in the CD player. 

The most telling part of this day in the life of music is that a medium was all but wiped out of existence by another medium of lower quality. For those who remember cassettes, yes, they were lower fidelity than vinyl records and far more portable, but they did not seal vinyl’s fate. CDs did. And while purists will win the argument that vinyl is of better quality than compact discs, there are too many variables that must be considered to preserve their case against the lowly 16-bit coaster. Vinyl’s superiority rests on many factors—the quality of the disc (180-gram virgin vinyl is the benchmark for great-sounding vinyl records), the quality of the turntable motor, the stylus, dust—just to name a few. CDs bear no such burden because they are digital. Once mastering and duplication engineers learned how to apply their craft for a digital medium, and once 20- or 24-bit DACs (Digital-to-Analog Converter – It is the hardware component in a CD player that converts the binary information on a CD into rock ‘n’ roll) became standard in even the cheapest CD players, CDs started sounding pretty good, all things considered.  

In my mind, a 24-bit CD format should have overtaken the current 16-bit format long ago. That was the next logical step, and one that happened on the production side more than a decade ago. In fact, I wonder if CD sales would be growing, or at least not shrinking, if that were the case. The original argument against this was that 24-bit CDs required a new 24-bit CD player. And 16-bit players were all they ever made in quantity. However, because of the way bit depths and DACs work, a 24-bit CD player could play all your old 16-bit discs, too—they might even sound better. And you could still rip them into any kind of download-friendly medium you wanted. The cost of making a 24-bit player would be nearly the same as that of a 16-bit player (better DACs would cost a few cents more). And the discs themselves would cost no more to produce, though they would hold less music since, at 24 bits, you’re adding an additional 6 Mbs per stereo minute. 

I think another factor that prevented 24-bit CDs from becoming a standard was that this higher bit depth was often married to a higher sample rate. Higher sample rates (96k is considered the sweet spot) are more technically challenging with regards to mainstream adaptability, and would really eat up space on the disc. Upon hindsight, I think CD producers and buyers would have been very satisfied with the improvements in bit depth alone. That even the most inexpensive home studio gear supports 24-bit, while the output medium never budged beyond 16, is another example of how record labels failed to lead in the digital world.  

As I’ve written about previously in Riot Gear!, bit depth in a waveform (audio in a digital format) is responsible for amplitude, and therefore dynamic range. Dynamic range is the difference between the noise floor (inherent noise generated by the electronics without any music being pumped through it) and the loudest possible undistorted signal. If you do the math, the available dynamic range for the 16-bit audio found on your CDs is about 96 dB (theoretically higher but technically lower). The human ear is capable of perceiving anywhere from 103 dB to 140 dB, depending on how many rock concerts you’ve attended sans earplugs.

Now here’s the rub: You’re only getting that 96 dB dynamic range from your audio CD if its waveforms (CD tracks) were recorded at full volume, meaning all 16 bits are used up. Well, even bad music has some dynamic range and headroom, so at 16 bits, you’re probably averaging 12 to 14 bits if you’re lucky and things are well-recorded.

The magic of 24-bit audio is that, even if you do not use all 24 bits, you are using at least 16 bits, probably more. So now your tracks have a dynamic range as good as or better than what we lowly humans can handle (24-bit audio has a dynamic range of about 144 dB). This spread is heard at the top and at the bottom. While maximum loudness is the same at 16 and 24, at the latter there is less chance of distortion and hard clipping by DACs struggling to keep up. At the bottom, the noise floor is well below what we can possibly hear. It also gives us enough bits for a sound to fade out before quantization errors kick in. This is what 24-bit and its wider dynamic range offers—more clarity, more expression, and the ability to retain some warmth because you have so many more levels of volume to work with and you can recorder hotter without the fear of hard clipping. And for those of us who work and play in digital, warmth is what is often missing. Put simply—greater bit depth equals greater sonic depth.

Even though we are making music at 24 bits (or sometimes higher), our end product will be that 16-bit CD (or an equally low-res downloadable file). Somehow, we have to ditch 8 bits to get to lucky 16. The choice is simple—truncate, or truncate and dither. Since this is digital, each bit in your 24- or 16-bit file contains either a zero or a one. If those last 8 bits (known by the politically incorrect term of least significant bits) had only zeros, then truncating is no big deal. But some of those bits have ones, and now they are (sniff, sniff) gone. And at that point where the truncation was made, your audio still had something to say, but now all it can say is a meek and plaintive fzzzt. We call that fzzzt a quantization error, which is a techy way of saying math boo boo). The end result—really crappyfzzt soundingfzzt digitalfzzt audiofzzt.      

Dither to the rescue.

Dither doesn’t really stop the truncation—after all, your world is now 16 bits, and no matter how hard you try, pouring 24 ounces of beer into a 16-ounce glass truncates 8 ounces all over your lap. What dither does, is add some very low level noise to the least significant bits, where the music is really quiet but still goddam important. This makes for a smoother transition from the sweet bits where the audio is nice and chunky, to the wee bits that no one loves because they have a tendency to go fzzzt. In affect, adding low-level noise fills those last bits with information that, in turn, pushes vital song information up into the higher more successful and popular bits. That fzzzt may still happen, but if it does it is masked by noise, or it happens at a level or frequency we cannot hear. The reason this all works is because our ears are smart. They ignore low-level noise when it is at a uniform frequency which lets us focus on the music in and above it. That’s why dithering works. Dithering also does something called noise shaping. Noise shaping strategically places the noise in and around certain frequencies, especially ones we don’t hear so well. So now those least significant bits will be making their offensive noises at frequencies we cannot hear or hear well.

In those subtle places where the hair stands up on the back of our necks while listening to a tune, dithering makes it happen as best it can considering it’s a 16-bit moment in a high resolution world (blasted downloads notwithstanding). We’re talking reverb tails, the last rings of a cymbal, and other sounds on the edges of silence—that’s where dithering is god.

The point I was trying to make before your eyes glazed over is that, of all the recording industry cock-ups in the digital age (and there are many), CDs not being allowed to evolve into a 24-bit medium is one of the biggest. Would it have saved the compact disc and the shuttering of record stores, the sound of which no amount of dithering can hide? Maybe. 24-bit is not a solution to downloading; it is an antidote, or at least a genuine alternative. Even though downloads are often lower quality than CDs, which I’ve used numbers to convince you aren’t much better, 24-bit audio would provide the differentiator that 16-bit CDs lack—and an accessible one. You don’t need to be an audiophile to appreciate the difference, nor do you need to invest in a high-end stereo. Face it: You were going to buy a new CD player at some point anyway, right?

I suppose it’s not too late, especially if someone puts me in charge (All hail King Dither!). But we’d better hurry. The news on the CD front is dire. And we already have enough monopolies fucking with the access and ownership of music.

Thanks to music stores shutting down, from mom and pop record shops to Virgin Megastores that have become such a small chain they can barely make a child’s bracelet, we’re going to have to rely on Amazon.com for our album purchases (which makes going without a record label that much easier). With labels rarely producing back catalogs anymore for non-mainstream or downstream artists (you know, the really good rock), expect to pay more than 16 bucks for their archive material. Christ, another sad ending… 

Max Mobley

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