Distortion in Digital Audio

Here’s a good article on digital audio.

The article explains a lot of things people who like music should know. First, we’ve all seen the “THD” or “total harmonic distortion” specs on all audio equipment. It turns out that harmonic distortion isn’t really an issue and it might even make music sound better. Violins have so many harmonics already, a little harmonic distortion is no big deal. Also, it’s a poor metric because digital devices are more prone to other types of distortion. It’s no surprise that they achieve <0.01% THD or something small like that, without much expense. It reminds me of $50 digital cameras with 14 MP that take awful pictures. Anyway, don’t buy audio gear based on the THD numbers. Now I wonder if maybe the expensive tube amps with poor THD numbers actually do sound better because they avoid the truly bad types of distortion that digital systems can create.

The article also does a great job of explaining quantization distortion and how dither turns it into quantization noise. Also, read about dither or at least look at the pictures so you’re clear on exactly how dither works and how amazing an idea it is:http://en.wikipedia.org/wiki/Dither

The article goes on to discuss 1-bit DSD, which I spoke highly of from a technical standpoint in this previous post. However, I agree with the authors that 24-bit or higher PCM is the best choice for audio processing and 1-bit DSD only makes sense as a final distribution medium. Any mathematical operations on 1-bit DSD are very complex and I don’t really know how the distortion and noise introduced will sound, but PCM is easy to understand.

I recently bought a couple pairs of high-end headphones. As the audio forums suggested, the headphones didn’t sound very good plugged into my computer’s soundcard. My ears felt fatigued after listening, despite low volumes. People on the forums say the poor quality is because sound cards or most digital players don’t have the power to drive large headphones. But they sounded bad even with the volume turned way down. Now, I think it’s more of an issue of quantization noise at low volumes. A D/A converter should receive the raw original bitstream, not scaled down, and then the volume adjustment should be an analog operation. I got a fairly inexpensive HeadRoom BitHead portable headphone amplifier / USB soundcard which makes the headphones sound great!

Also, the more I’ve learned and listened, the more I think that mp3 audio may in fact be of sufficient quality or even indistinguishable from CD, SACD or DVD-Audio. The inadequate sounding mp3′s I’ve heard are probably that way because the original recording or mastering was poor, not a fault of the compression. It is possible to get a crisp, clear, precise sound from an mp3. A bad D/A conversion system probably does more audible harm than the mp3 compression.