question about harmonics (last one, promise) *PIC*

[unknownuser]

Sorry, I just don't know anything about musical instruments or their harmonics! Well, I do understand how to calculate harmonics, but I don't understand what the instructor is asking here, any help appreciated =) (I know, I have no idea what this has to do with a course titled "digital audio" either, deffinetly can't find this in my book anywhere.)

I believe the answers to be ...

11) 2nd and 4th harmonic

12) 3rd harmonic

13) not sure, I notice that PLUCK is all in caps .. guessing only the 4th harmonic will be heard.

Thanks again!


(Originally posted by: dev13)

[steve_r]

> Sorry, I just don't know anything about
> musical instruments or their harmonics!
> Well, I do understand how to calculate
> harmonics, but I don't understand what the
> instructor is asking here, any help
> appreciated =) (I know, I have no idea what
> this has to do with a course titled
> "digital audio" either, deffinetly
> can't find this in my book anywhere.)

> I believe the answers to be ...

> 11) 2nd and 4th harmonic

> 12) 3rd harmonic

> 13) not sure, I notice that PLUCK is all in
> caps .. guessing only the 4th harmonic will
> be heard.

> Thanks again!

I agree with your answers for 11 and 12. For 13, the key is that plucking the string at point C means it will have a maximum amplitude at that point, therefore there can't be a node. If my reasoning is correct, I believe the result would be the second harmonic.

[unknownuser]

> I agree with your answers for 11 and 12. For
> 13, the key is that plucking the string at
> point C means it will have a maximum
> amplitude at that point, therefore there
> can't be a node. If my reasoning is correct,
> I believe the result would be the second
> harmonic.

hmmm, I see what you're saying .. wouldn't that put it 180 out of phase at the second harmonic then however?


(Originally posted by: dev13)

[dastardly]

> I agree with your answers for 11 and 12. For
> 13, the key is that plucking the string at
> point C means it will have a maximum
> amplitude at that point, therefore there
> can't be a node. If my reasoning is correct,
> I believe the result would be the second
> harmonic.

No... Has to be at least the 1st harmonic. And, I am pretty certain all harmonics.

Just from empirical evidence about 1/4 of the way is exactly where a person actually plucks/strums a guitar, so empirically the answer must be at least the first harmonic.

I say all because there have been quite a few times that I have seen spectrum analyzers of sounds and they have always shown all harmonics to the sensitivity level of the analyzer.

By the way are you only allowed to use the harmonics on the paper? Because if not all your answers are wrong. The first one is all even harmonics. Yes, the higher order harmonics have very little energy and probably are damped very quickly, but they are allowed to vibrate. And of course the second one is all harmonics that are multiples of 3 with the same caviat about the higher order harmonics from the previous answer.

What this has to do with a course titled "digital audio"? Digital audio by definition is sampled. Typically CD's are samples at 44kHz. What you will probably learn next is that at 44kHz sample rate the only sounds that can be accurately digitized are those below 22kHz. Those above 22kHz will be aliased. I would guess that could lead to some very weird effects if there were some high amplitude ultrasonic getting to the digitizer. Which would suggest that it would be important to include a 22kHz low pass filter on the analog front end to an audio digitizer. This also tells you how many of the higher order harmonics will not be reproduced by digital recording. But, human hearing only goes to 20kHz (give or take) and high order harmonics tend to have little energy, so little is lost.

[unknownuser]

> No... Has to be at least the 1st harmonic.
> And, I am pretty certain all harmonics.

> Just from empirical evidence about 1/4 of
> the way is exactly where a person actually
> plucks/strums a guitar, so empirically the
> answer must be at least the first harmonic.

> I say all because there have been quite a
> few times that I have seen spectrum
> analyzers of sounds and they have always
> shown all harmonics to the sensitivity level
> of the analyzer.

That makes sense, thanks.

> By the way are you only allowed to use the
> harmonics on the paper? Because if not all
> your answers are wrong.

Right, I realise the 1st question would be the 2nd, 4th, 6th, 8th, harmonic to infinity, but he just wants the responces to reflect what's on the paper.

> What this has to do with a course titled
> "digital audio"? Digital audio by
> definition is sampled. Typically CD's are
> samples at 44kHz. What you will probably
> learn next is that at 44kHz sample rate the
> only sounds that can be accurately digitized
> are those below 22kHz. Those above 22kHz
> will be aliased. I would guess that could
> lead to some very weird effects if there
> were some high amplitude ultrasonic getting
> to the digitizer. Which would suggest that
> it would be important to include a 22kHz low
> pass filter on the analog front end to an
> audio digitizer. This also tells you how
> many of the higher order harmonics will not
> be reproduced by digital recording. But,
> human hearing only goes to 20kHz (give or
> take) and high order harmonics tend to have
> little energy, so little is lost.



(Originally posted by: dev13)