Subject: Re: Re[2]: [linux-audio-dev] peakfiles and EDL's
From: Robert Schrem (Robert.Schrem_AT_WiredMinds.de)
Date: Thu Mar 01 2001 - 22:15:47 EET
>>
>> > Speech waveforms in particular can be very asymmetric, so if you want
>> > the peakfile display to look the same as the zoomed-out waveform you
>> > need + and - peaks.
>>
>> Well, you will not be able to make percise zero crossin cuts
>> from peak file information anyway. You would have to zoom in
>> and then you will see the real sample data anyway.
>
> I was talking about the asymmetry of speech waveforms over tens or
> hundreds of cycles, not just from one half of a cycle to the next.
>
>> The peak file 'waveform' display woun't look similar like the
>> real data. For an explantation why, look for my detailed
>> email a few day's back... :)
>
> But the peak file *will* look like the real data...
>
> Think of an oscilloscope - when the timebase is short you can clearly see
> the waveform. As you turn the timebase to longer times, the waveform is
> drawn very slowly across the screen, and you might not see each individual
> cycle, just the envelope - the maximum and minimum ampitudes.
Yust my two cents: Yes, you would see the envelope of the
signal - but an envelope of an signal and the signal curve in
detail will not look similar to me in many cases... If you
zoom out very far you will see always a rectangle whatever the
original signal was... It woun't be possible to distinguish a
sine from a square wave... That's what I meant.
You would also not be able to juge from peak file data
where the signals crosses zero - remember we compute a peak
file data value all 2048 samples. It would be pretty usual
to observe several zero crossings in a range of 2048 samples.
> When you are zoomed out on a computer display, you don't want to waste
> time drawing thousands of samples, up and down over the same column of
> pixels, before moving to the next column and drawing thousands more - you
> can save time and get the same result using a peakfile.
We agree on this, don't we?
>
>
> Paul.
>
> -----------------------------
> m a x i m | digital audio
> http://www.maxim.abel.co.uk
> paul.kellett_AT_maxim.abel.co.uk
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