This is an interesting video, and for their stated purpose (to dispel the idea that the output of a D/A converter is a stairstep) it's great. But, to be fair, he's only addressing one part of the process (the conversion from analog to digital and back). Arguments about "analog" and "digital" in recording tend to include such things as tape saturation, transformers, vinyl cutting technique, floating-point error, plugin aliasing, etc which are separate issues from A/D and D/A and are as much about what "sounds good" as about whether a sampled signal can be perfectly reconstructed. Also, the demonstrations with the oscilloscope are illuminating regarding the math behind digital audio, but those aren't exactly precision measurements. There are real effects due to clock jitter on both the A/D and D/A end that can cause small but measurable distortions. "Ideal" sampling and reconstruction requires "ideal" hardware, which (as you might guess) doesn't exist! The amount of "non-ideal" behavior may not bother you, for any particular value of "you", but then again it may. Thanks, Bill Gribble On Wed, 2013-05-22 at 15:08 +0100, Barney Holmes wrote:

On Wed, May 22, 2013 at 10:38:37AM -0400, Bill Gribble wrote: Not to mention audible if it's severe enough. Decimation filters that only give 6 or 12dB attenuation at fs/2 (typical in many pro audio ADC chips) can allow audible aliasing too. I wouldn't expect an oscilloscope to have enough resolution to detect these effects, but a good spectrum analyser and/or a good pair of ears often can. John

On Thu, May 23, 2013 at 09:38:40AM +0200, Jörn Nettingsmeier wrote: Most of the DSP textbooks I own refer to down-sampling as decimation and up-sampling as interpolation. I guess it depends on context. I meant the anti-alias filter used in the down-sampling stage of an oversampling ADC. Many ADC manufacturers use the same term on their data sheets (not that it excuses my laziness ;-)). Data sheets for ADC chips commonly used in pro audio applications typically list stop band attenuation at 0.55fs, where they give impressive attenuation figures. At 0.5fs the attenuation can be much lower. As an example, take the TI PCM4222. The data sheet shows a stop band attenuation of -100dB at 0.546fs for the "classic" filter response setting (there is also a low group delay setting with lower attenuation). However, a look at the frequency response graph shows the attenuation at 0.5fs is only around -10dB. Many of the commonly used ADCs show a similar response, but not all manufacturers provide this information. There's an excellent paper by the late Julian Dunn describing the problem: http://www.nanophon.com/audio/antialia.pdf Section 3 goes into detail on inadequate filter rejection. Some of the figures listed for real ADCs are pretty shocking. Section 4 discusses related problems in DAC anti-imaging filters. John

On Thu, May 23, 2013 at 12:18:25PM +0000, Fons Adriaensen wrote: True, although I'd have more confidence in a filter that eliminated the possibility entirely. I couldn't resist responding to the statement in the thread title: "No difference between analog and digitally processed sound". As in so many things, "that depends". John