[sdiy] Harmonic bandwidth

[Tom Wiltshire]

On 9 Jan 2008, at 16:45, Ian Fritz wrote:

> Here are a couple more things to think about.
>
> Room acoustics:  If you play a sawtooth through your speakers you  
> will hear the timbre change as you move your head around.  If you  
> change the phases of the harmonics, then you are introducing  
> different delays which translate to different relative spatial  
> positions of the wave components' loops and nodes. So I think you  
> may hear differences just because of that effect.

I agree that this is a possible explanation, but if it were true,  
then we shouldn't have been told that the human ear can't hear phase,  
since we'd be able to hear phase differences as relative spatial  
positions. So it might be so, but it doesn't explain the discrepancy  
between experiment and theory.


> Speaker dynamics: If you put a perfect sawtooth into a speaker you  
> would be asking for its displacement to change instantaneously.  If  
> you rephased the harmonics then you would no longer have this  
> step.  Of course you never have exactly this situation, but the  
> transient mechanical response of the speaker to a step should be  
> kept in mind.  For this reason I think the sawtooth does not make a  
> very good test.

We can use any collection of harmonics you like! We've all got  
additive-wave-generating scripts written now!

> An old trick of loudspeaker salesmen is to play at a higher level  
> through the speakers they want to sell.  There was a very large  
> loudness difference in the first pair of examples that were  
> posted.  It is very important when comparing timbre to keep the  
> loudness level the same, probably to within 0.5 dB.

Sorry Ian, but what counts as 'the same loudness'? You're not talking  
about peak level, since the first pair of examples had the same peak  
level, although the average level might have been different, and you  
say there was a loudness difference.
I'm not trying to nit-pick, I just don't understand what you mean by  
'loudness' in a technical sense. What parameter of the waveform is  
'loudness'?
I'm sure I can normalise all the phase-altered samples to the same  
loudness to some arbitrary degree of accuracy once I know what I'm  
doing!

T.