[78-L] waveforms

[Wes]

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 

> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Date: Tue, 15 Jan 2013 16:07:09 -0800 (PST)
> From: DAVID BURNHAM <burnhamd at rogers.com>
> Subject: [78-L] waveforms
> 
> Here's a question for the techies. I'm looking at a wave form of a?
> recording of human voice. (not whale singing).
> 
> The amplitude of the positive part of the waveform is higher than the?
> negative side.
> 
> What causes this? How does this affect the sound? And is there a fix,?
> assuming it is needed?
> --?
> Joe Salerno
> 
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> This is perfectly normal and requires no fix. ?While the positive and 
> the negative halves contain the same amount of energy, the positive 
> half contains more high frequency content than the negative half. ?
> This is true of any audio signal; if you take a single cycle of the 
> waveform and somehow measure the enclosed area of the positive 
> half and the negative half, (don't ask me how to do this), you'll 
> find the enclose areas are identical. But the high frequency 
> components of the positive half will have a higher amplitude, 
> hence they'll appear to be higher than the depth of the negative 
> half. ?This is why it's important that your speakers are connected 
> in such a way that the positive half of the waveform produces a 
> compression of air, a positive transient will travel in air much 
> more efficiently than a negative transient, (try sucking out birthday 
> candles rather than blowing them out). You may ask how we 
> know that there's the same amount of energy in the positive 
> halves and the negative halves if we have no way of measuring 
> it, (maybe there is a way but I don't know about it), the answer 
> is simply that every sound producing device, be it a musical 
> instrument or a speaker, comes back to its rest position when 
> the sound ends, hence all of its positive travels and negative 
>travels are equal. ?
> 
> db