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  #1  
Old 04-13-2010, 12:30 AM
votard votard is offline
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Default i don't know a good title for this....

....so I made two square waves - 40hz and 41hz- in audacity and played them both at the same time and it has this weird effect. what is this? is this phasing(if not, can somebody explain phasing to me?)?
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Old 04-13-2010, 01:04 AM
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Default Re: i don't know a good title for this....

pitch modulation or bending probably. phasing I think is time based where the waves arrive at the same point a split second apart.
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Old 04-13-2010, 01:06 AM
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Default Re: i don't know a good title for this....

My guess would be the normal effect of dissonant notes clashing.
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Old 04-13-2010, 02:46 AM
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Default Re: i don't know a good title for this....

Well, i'm not sure if 40 and 41 fall on a chromatic scale, but if they do, i'd guess they'd be just a half step apart which would be a tri-tone.
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Old 04-13-2010, 02:58 AM
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Default Re: i don't know a good title for this....

Quote:
Originally Posted by diosdude View Post
Well, i'm not sure if 40 and 41 fall on a chromatic scale, but if they do, i'd guess they'd be just a half step apart which would be a tri-tone.
I'm pretty sure those two frequencies are too close together to be in the same scale,

40 - 41 is friggin LOW. You would feel it more than hear it
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Old 04-13-2010, 03:39 AM
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Default Re: i don't know a good title for this....

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Originally Posted by larryace View Post
My guess would be the normal effect of dissonant notes clashing.
Bingo. Sometimes guitar players will do this by playing the same high pitched harmonic on two different strings at the same time and then dive bombing slowly with the tremolo. The two harmonics go down in pitch at different rates and as the frequencies diverge it creates a building dissonance.
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Old 04-13-2010, 09:27 AM
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Default Re: i don't know a good title for this....

From a physics point of view, what you heard is called a Beat and is caused by alternating constructive and destructive interference between the two waves. So even when you're not drumming you're creating beats... how cool is that. Anyway, here's a detailed explanation.
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Old 04-13-2010, 10:15 AM
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Default Re: i don't know a good title for this....

Philly's got it. The principle is more or less the same as playing 7/4 against 4/4 one time sig against another, and there will be a noticeable moment every 28 bars where it all lines up.

I've attached a brief MP3 of the tones 40, then 41, then both together. If you look at the waves in Audacity you'll see that compressing to MP3 distorts the square waves.
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File Type: mp3 tones.mp3 (128.4 KB, 142 views)
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Old 04-13-2010, 10:56 AM
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Default Re: i don't know a good title for this....

The closer the two frequencies are, the more distinguishable the beat characteristics. Polly's sound file is a pretty good display of this phenomenon. For two sine waves with frequencies f1 and f2, you will get a wave with frequency (f1+f2)/2, so the average of the frequencies. The amplitude of this wave will be modulated with frequency (f1-f2)/s, so half the difference in frequency. For 40 and 41Hz you'd get a tone of 40.5Hz modulated in amplitude with a frequency of 0.5Hz in the case of sine waves. Rectangular waves are a different story as the waves themselves are a big series of sine waves summed together to create a rectangular wave (see the Fourier Series for more information on this - it's actually pretty cool.

Last edited by Big_Philly; 04-13-2010 at 12:26 PM.
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Old 04-13-2010, 08:05 PM
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Default Re: i don't know a good title for this....

Quote:
Originally Posted by Big_Philly View Post
The closer the two frequencies are, the more distinguishable the beat characteristics. Polly's sound file is a pretty good display of this phenomenon. For two sine waves with frequencies f1 and f2, you will get a wave with frequency (f1+f2)/2, so the average of the frequencies. The amplitude of this wave will be modulated with frequency (f1-f2)/s, so half the difference in frequency. For 40 and 41Hz you'd get a tone of 40.5Hz modulated in amplitude with a frequency of 0.5Hz in the case of sine waves. Rectangular waves are a different story as the waves themselves are a big series of sine waves summed together to create a rectangular wave (see the Fourier Series for more information on this - it's actually pretty cool.
Mr Spock called and said he wants his brain back.

To the O/P...uh...yeah...I was going to say that too, but Big Philly beat me to it.
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Old 04-13-2010, 09:26 PM
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Default Re: i don't know a good title for this....

Could this be the mysterious brown note?
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Old 04-14-2010, 11:19 PM
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Default Re: i don't know a good title for this....

Quote:
Originally Posted by diosdude View Post
Mr Spock called and said he wants his brain back.
It's actually quite elementary physics / mathematics (the beat phenomenon - Fourier Series are advanced calculus material). Not even Spock-ish by a long shot.
I hold a Bachelor of Science degree, my BSc assignment was in the field of acoustics so I can consider myself knowledgeable on wave phenomena :)
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Old 04-19-2010, 12:01 AM
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Default Re: i don't know a good title for this....

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Originally Posted by larryace View Post
40 - 41 is friggin LOW. You would feel it more than hear it
Square waves (and sawtooth waves) aren't as subtle as sine waves in that sense.

That article on the fourier series was interesting and I think I got the gist of it from the pictures lol, but all that math was yucky. D:
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Old 04-20-2010, 12:36 PM
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Default Re: i don't know a good title for this....

Quote:
Originally Posted by diosdude View Post
Well, i'm not sure if 40 and 41 fall on a chromatic scale, but if they do, i'd guess they'd be just a half step apart which would be a tri-tone.
They're far far closer together than chromatic notes. Also, tri-tone is six semitones or three steps apart, e.g. C to F sharp, not a half step.
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