24/192 Music Downloads Are Very Silly Indeed (2012)
Good points in the article, but it has some flaws.<p>The problem whenever somebody writes about digital audio, is that it is very tempting to hold on to sampling <i>theory</i> (Nyquist limit, etc) and totally discard the problems of implementing <i>an actual Analog-Digital and Digital-Analog chain</i> that works perfectly <i>at 44100Hz sample rate.</i><p>I agree with the assesment that 16 bit depth is good enough; even 14 bit is good enough and was used with good results in the past (!). However, the problem is with the sampling rate.<p>&gt; <i>All signals with content entirely below the Nyquist frequency (half the sampling rate) are captured perfectly and completely by sampling;</i><p>Here lies the problem. This is what <i>theory</i> says, however, when using 44KHz sample rate, this means that to capture the audio you need to low-pass at 22KHz. And this is not your gentle (6, 12 or 24db) low-pass filter; no, this needs to be HARD filtering; nothing should pass beyond 22KHz. And this must be on the analog domain, because your signal is analog. To implement such a filter, you need a brickwall analog filter and this is not only expensive, but it also makes mess with the audio, either &#x27;ringing&#x27; effects and&#x2F;or ripple on the frequency response and&#x2F;or strong phase shifts.<p>So on Analog-to-digital in 2017, converters should be operating at a higher rate (say, 192KHz), because this makes analog filtering of the signal much easier and without side effects.<p>Now, for Digital-to-Analog, if your sample rate is 44KHz, you have two alternatives:<p>a) Analog brickwall filtering, with the problems noted above<p>or<p>b) filtering on the digital domain + using oversampling<p>the article mentions:<p><i>&gt;So the math is ideal, but what of real world complications? The most notorious is the band-limiting requirement. Signals with content over the Nyquist frequency must be lowpassed before sampling to avoid aliasing distortion; this analog lowpass is the infamous antialiasing filter. Antialiasing can&#x27;t be ideal in practice, but modern techniques bring it very close. ...and with that we come to oversampling.&quot;</i><p>So they are mentioning alternative (b). The problem is that oversampling does not solve all problems. Oversampling implies that the filtering is done on the <i>digital</i> domain and there are several choices of filtering you could use, for example FIR (Finite Impulse Response), IIR (infinite impulse response), etc.<p>And each one of these choices have side effects...<p>In short, the problem is that with 44KHz sampling rate, your filter cutoff (22KHz) is too short to your desired bandwidth (20Hz-20KHz). Using a sample rate of 192KHz gives the DAC designer much more leeway for a better conversion. And CONVERSION is the key to good digital sound.<p><i>&gt;What actually works to improve the quality of the digital audio to which we&#x27;re listening?</i><p>It is interesting that the author mentions things such as &quot;buying better headphones&quot; (agree), but he <i>never</i> mentions &quot;Getting a better Digital to Analog converter&quot;, which is highly important !!<p>On the other hand, he backs up his claim that &quot;44KHz is enough&quot; with an interesting AES test i was already aware of in the past:<p><i>&gt;Empirical evidence from listening tests backs up the assertion that 44.1kHz&#x2F;16 bit provides highest-possible fidelity playback. There are numerous controlled tests confirming this, but I&#x27;ll plug a recent paper, Audibility of a CD-Standard A&#x2F;D&#x2F;A Loop Inserted into High-Resolution Audio Playback, done by local folks here at the Boston Audio Society.</i><p>This is a very interesting paper, and I did have the copy, however the test equipment should be checked. There are systems and better systems. The AES paper cited above had the particularity that the ADC and DAC used were provided by exactly the same machine (a Sony PCM converter), with the same strategy: no oversampling, brickwall analog filters. I can bet (99% sure) that the brickwall filters were identical on the ADC and the DAC on that machine; Murata-brand filters in a package.<p>The devil, as they say, is in the details.