Today I made a test cd with among other things, a 1kHz square wave. Looking at on a scope showed the ringing that is often described when a CD player tries to reproduce a square wave. This is often blamed on the sharp rollof (and therefore high Q) of the low pas filter that lets below 20kHz pass, but more or less stops the 44.1 kHz getting through. Of course oversampled dac's have a higher sampling frequency and so need a less sharp filter but that's a different story.
Anyway, I got to thinking about all this, and while any ringing after the vertical transition is understandable, what I also saw is some ringing building in amplitude just before the transition as well. Now I generated the square wave using Cool Edit 96 and I suppose it constructs the waveform by adding odd harmonics and this is what you see in the pre-ringing and post-ringing, but to blame any pre-ringing on the sharp cutoff low pass filter after the dac is ridiculous because the filter cannot know that a transition is coming and start to get all wobbly! I have seen again and again people whingeing and whining about rotten square waves coming out of cd players, and as "evidence" they show a pic of one of these pre and post ringing square waves.
Post ringing from crook filters I can believe, but pre-ringing ? No way!
GP.
P.S. This pre-ringing could also be seen right at the dac output too, BEFORE the filter.
Also, here's an ascii output of the Cool edit file. As you can see, there is no pre-ringing in it.
Left and right channels, 1 kHz, -3dB level, 44.1kHz sample rate.
23198 23197
23197 23197
23197 23197
23198 23198
23198 23198
23197 23197
23197 23197
23197 23198
23197 23197
23197 23197
23197 23197
23198 23198
23197 23197
23197 23197
23197 23197
23197 23197
23197 23197
23198 23197
23197 23197
23198 23197
-23198 -23197
-23197 -23198
-23197 -23197
-23197 -23197
-23197 -23197
-23198 -23197
-23198 -23197
-23198 -23197
-23198 -23198
-23198 -23197
-23197 -23198
-23197 -23197
-23197 -23197
-23197 -23197
-23198 -23197
-23197 -23197
-23197 -23197
-23197 -23197
-23197 -23198
-23197 -23197
-23198 -23198
-23198 -23196
23197 23198
23198 23197
23197 23197
23197 23197
23198 23197
23197 23198
23197 23197
23197 23197
23198 23197
23198 23197
23198 23197
23197 23197
23197 23197
23197 23197
23198 23198
23197 23197
23197 23198
23197 23197
23198 23198
23196 23196
23198 23197
23197 23197
-23197 -23197
-23197 -23198
-23198 -23196
-23197 -23196
-23197 -23198
-23197 -23197
-23197 -23197
-23197 -23197
-23197 -23198
-23198 -23198
-23198 -23197
-23197 -23197
-23198 -23197
-23197 -23197
-23197 -23197
-23197 -23197
-23197 -23198
-23198 -23197
-23197 -23198
-23197 -23197
-23198 -23197
-23197 -23197
23198 23197
23197 23197
23197 23197
23197 23197
23198 23197
23198 23197
23198 23198
23197 23198
23197 23197
23197 23198
23198 23197
23197 23197
23197 23197
23198 23197
23198 23197
23197 23197
23197 23198
23197 23198
23198 23197
23197 23197
23197 23197
23197 23197
-23197 -23197

Anyway, I got to thinking about all this, and while any ringing after the vertical transition is understandable, what I also saw is some ringing building in amplitude just before the transition as well. Now I generated the square wave using Cool Edit 96 and I suppose it constructs the waveform by adding odd harmonics and this is what you see in the pre-ringing and post-ringing, but to blame any pre-ringing on the sharp cutoff low pass filter after the dac is ridiculous because the filter cannot know that a transition is coming and start to get all wobbly! I have seen again and again people whingeing and whining about rotten square waves coming out of cd players, and as "evidence" they show a pic of one of these pre and post ringing square waves.
Post ringing from crook filters I can believe, but pre-ringing ? No way!
GP.
P.S. This pre-ringing could also be seen right at the dac output too, BEFORE the filter.
Left and right channels, 1 kHz, -3dB level, 44.1kHz sample rate.
23198 23197
23197 23197
23197 23197
23198 23198
23198 23198
23197 23197
23197 23197
23197 23198
23197 23197
23197 23197
23197 23197
23198 23198
23197 23197
23197 23197
23197 23197
23197 23197
23197 23197
23198 23197
23197 23197
23198 23197
-23198 -23197
-23197 -23198
-23197 -23197
-23197 -23197
-23197 -23197
-23198 -23197
-23198 -23197
-23198 -23197
-23198 -23198
-23198 -23197
-23197 -23198
-23197 -23197
-23197 -23197
-23197 -23197
-23198 -23197
-23197 -23197
-23197 -23197
-23197 -23197
-23197 -23198
-23197 -23197
-23198 -23198
-23198 -23196
23197 23198
23198 23197
23197 23197
23197 23197
23198 23197
23197 23198
23197 23197
23197 23197
23198 23197
23198 23197
23198 23197
23197 23197
23197 23197
23197 23197
23198 23198
23197 23197
23197 23198
23197 23197
23198 23198
23196 23196
23198 23197
23197 23197
-23197 -23197
-23197 -23198
-23198 -23196
-23197 -23196
-23197 -23198
-23197 -23197
-23197 -23197
-23197 -23197
-23197 -23198
-23198 -23198
-23198 -23197
-23197 -23197
-23198 -23197
-23197 -23197
-23197 -23197
-23197 -23197
-23197 -23198
-23198 -23197
-23197 -23198
-23197 -23197
-23198 -23197
-23197 -23197
23198 23197
23197 23197
23197 23197
23197 23197
23198 23197
23198 23197
23198 23198
23197 23198
23197 23197
23197 23198
23198 23197
23197 23197
23197 23197
23198 23197
23198 23197
23197 23197
23197 23198
23197 23198
23198 23197
23197 23197
23197 23197
23197 23197
-23197 -23197