The Logic Off Topic list

>Dennis Gunn <dennisg@...> wrote:
>
>>Once about 9 years ago on the DAW I remember writing about how the
>>digital wave form for a sine wave up around say 19.k looks like a
>>broken spiral staircase and how I find it hard to believe that any
>>amount of filtering is going to turn that into a clean sine wave.
>
>Nine years is a long time in the history of DAWs...

Yes it is. But I think it was about nine years ago I bought one the 
first batch of audio media cards that came out and was using the very 
first versions on Studio Vision.  Was it less?  Maybe.


>It is entirely feasible to digitally filter a square wave to produce a
>sinewave within the practical limits of a digital systems parameters,
>which is effectively what is going on in what you describe above.

No  a square wave isn't what I am describing and if you have ever 
looked at the digital data for a 19k sine wave in a 44.1k pcm signal 
then you know what I mean.  It looks like there will be resonances at 
other frequencies and as a matter of fact with most digital 
synthesizers I have ever used especially the older ones I can hear 
those resonances as undertones in what should be pure high 
frequencies.


>In any case, why is it hard to believe? Isn't filtering one of
>the cornerstones of sound processing? Was Fourier wrong??

I don't know if he was wrong or right but I am pretty sure that his 
mathematics describe something that is difficult to manifest 
perfectly in an audio circuit in the real world and it is my opinion 
that plays a significant factor in the character that we all hear in 
digital audio that makes it a little less than the "perfect" 
recording medium we all dreamed it would be way back when it was new.

>The problem lies in allowing >> nyquist frequencies to get to the
>the output, as for example would happen in an unfiltered saw or
>square oscillator at even modest frequencies with a less than ideal
>filter at the converter stage. Better filter implementaions,
>Greater sample rates and higher bit depths allwork to minimise this
>problem...
>
>>A
>>lot of peaple called me ignorant for being decieved by the look of
>>data but Nothing I have seen or heard since has ever convinced me I
>>was wrong.
>
>Though I don't entirely disagree with you, from what I have learned of
>you on this list I don't find that statement a complete surprise.

So your saying I am not wrong but I should be?  You are pretty 
consistent yourself.