[78-L] waveforms

[neechevoneeznayou at gmail.com]

I was not referring to a lissajous waveform, only a simple waveform. 
Sorry I don't know another name for this. The kind of image seen in 
Audacity, for example. Audition calls it a waveform view, as opposed to 
spectral view.

joe salerno


On 1/17/2013 10:10 PM, DAVID BURNHAM wrote:
> Sorry folks, but I really must challenge what David Burnham has written.
>
> Joe: When you say waveform, what you actually mean is you are looking at a
> few cycles of the dominant frequency. If you scan through the waveform
> you'll find it changes shape within milliseconds. Imagine if you had some
> mains hum on the audio (say 50Hz 'cos the maths is easier). You'd need to be
> looking at at least 20 milliseconds (the wavelength of a single 50Hz cycle)
> to be able to see the effect of the hum, which would be a rise and fall in
> the centre point of the dominant frequency waveform. The human voice is very
> complex and contains a very
>   wide range of frequencies including breathing
> and chest resonance, so looking at the dominant frequency isn't the full
> picture.
>
> David: Energy doesn't have positive and negative. If you push or pull
> something you are always using energy. Perhaps force is a better
> description? But to continue with your terminology - the positive and
> negative half cycles don't necessarily contain equal "energy" on a per cycle
> basis. The only thing that we can say is that the sum of the "energy" in the
> two parts of the cycle approaches zero as they are summed over a long
> period. As a mathematician might say it TENDS to zero as time TENDS to
> infinity.
>
> .. wes
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Hi Wes
>
> I assumed Joe was looking at a lissajous waveform on a scope.  I don't know whether the correct term is energy or force, (Michael Biel, for whom I have huge respect, leaves me licking my wounds if I use the term "phase" when I should have said "polarity"), but electronic audio waveforms can, for any number of reasons, have a DC offset, but this always indicates a problem in audio, (not in video), but I don't think this is what Joe is referring to.  On a scope with horizontal sweep, the baseline would move up or down from the centre if there was a DC element;  a lissajous pattern will also move up or down along the mono axis.  But after seeing exactly what Joe is talking about on scopes for so many years I believe this is just the natural appearance of complex voice and music audio waveforms.  When I say that the positive half of the waves contain more of the high frequency components, I'm referring to the fact that you'll see sharper higher peaks in
>   the positive half of the wave compared to the more rounded features of the negative half.  In nature, most if not all sounds begin with a compression of air.  In speech explosive consonants such as t p b k d also start with a compression.  Some sounds like brass, (expecially muted trumpet or trombone), have a very sharp positive peak many dB higher than the waveform overall.  I don't want to start repeating myself but I think it's recogniized that positive compressions of air travel much more efficiently than negative rarefactions.  Going back to the birthday candles, if you aim a short compression of air at a candle, the flame will flicker at a distance of 15 feet or more, (after a delay);  aim a rarefaction of air, (a short inhale), and you'll have trouble disturbing a flame a foot away.
>
> db
> _______________________________________________
> 78-L mailing list
> 78-L at klickitat.78online.com
> http://klickitat.78online.com/mailman/listinfo/78-l
>

-- 
Joe Salerno