Musical Soundwaves

[Ron Overs]

Greetings Terry,

You wrote:

>Why does a flute sound like a flute? Why does an obo sound like an 
>obo? Why does a guitar sound like a guitar? And last, but certainly 
>not least, why does a piano sound like a piano?
>
>Does anyone have a simplistic explanation for what is the cause of 
>unique sounds/tones among various instruments? If you play A4 at a 
>pitch of 440 Hz on any instument, you will hear the pitch of 400 Hz. 
>But they will all sound different. So I guess they all do something 
>different to the soundwave that reaches your ear. What is that 
>difference? How does a speaker reproduce these differences of they 
>only move in and out?

Basically, all musical instruments will tend to produce tone with the 
harmonics or partial series present with the fundamental tone. Even a 
flute, which has a more pure tone than many instruments, still has 
harmonic content. The volume of the partials relative to that of the 
fundamental tone will vary from one type of instrument to another. 
Just try the simple test of holding down a piano note to lift the 
damper, while playing the notes which most closely match the 
frequencies of the harmonic series for the held note, ie, octave, 
octave and fifth, double octave, double octave and a third, " and a 
fifth, " and a seventh, triple octave. You will notice that some 
harmonics induce much more strongly into the held note than others. 
This variability will reflect the harmonic content of 'piano' tone. 
If it were possible to conduct a similar test with another type of 
instrument, you would find that the harmonic content would be 
slightly different, according to the tonal characteristics of that 
instrument.

The reason why A440 sounds like A440 on a piano, voice and mandolin, 
is that our ear locks onto the lowest frequency, the fundamental, to 
identify the pitch of the note. So while the tonal characteristics of 
the instruments might be very different, an A440 played on each 
instrument will still cause our ears to identify the pitch for what 
it is. One reason why it is very difficult to discern the pitch of 
note A1 on a short piano, is that there is virtually no fundamental 
tone present. Furthermore, the harmonic content will have such high 
inharmonicity, that a serious pitch crisis will exist between the 
fundamental tone and the harmonics, to make pitch identity even more 
difficult. Try this simple test, on a concert piano play the lowest 
minor third C to A, then repeat the same test on a 'sawn off' piano. 
The minor third interval is easy to hear on the concert instrument, 
but nearly impossible to discern on the shorter 'sawn off' variety.

While the harmonic content variability allows our ears to discern 
which particular instrument the tone is coming from, as some other 
writers have mentioned, the decay and attack characteristics will 
also vary according to the instrument in question. Furthermore, 
inharmonicity also introduces an added dimension to the 
characteristics we hear.

I also suspect that when sampled tones are recorded, the volume of 
the harmonics is reproduced faithfully but not the inharmonicity. If 
this is the case, it would readily explain why sampled piano sounds 
do not sound exactly like pianos. Does anyone else have something to 
add to this? If this is not correct regarding sampled tone I would 
appreciate a subsequent post on the matter.

Best,
Ron O.
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Grand Piano Manufacturers

Web: http://overspianos.com.au
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