Gil missFlag
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#1
2nd February 2013
Old 2nd February 2013
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LFO harmonics?

This is something I've always wondered and never really had an answer for.

Why is it that if you tune a sawtooth to a very low frequency, below audio range, (say 10hz) all you hear is a bunch of clicks at the start of each waveform cycle, and not the harmonics of the sawtooth which technically should be in the audible range (20hz, 30hz, 40hz, 50hz etc.)? Why is it that the fundamental frequency has to be in the audio range for us to hear all the harmonics?

I mean, if I were to reconstruct a sawtooth using additive synthesis and sine waves, there's no reason why I wouldn't hear the harmonics above the fundamental, so how is this different?
Tuesday Knight
#2
2nd February 2013
Old 2nd February 2013
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I would say due to the downwards slope of those higher harmonics in amplitude, i could be wrong, ever seen how you draw a saw wave in a additive synth (in amplitude).

Not sure, I've never listened to it apart from when I've plugged something in wrong.
#3
2nd February 2013
Old 2nd February 2013
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Quote:
Originally Posted by Gil missFlag View Post
I mean, if I were to reconstruct a sawtooth using additive synthesis and sine waves, there's no reason why I wouldn't hear the harmonics above the fundamental, so how is this different?
it's not different. if you were to construct a saw wave out of sines, you would get the exact same result...a saw wave.
Gil missFlag
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2nd February 2013
Old 2nd February 2013
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Quote:
Originally Posted by stinkyfingers View Post
it's not different. if you were to construct a saw wave out of sines, you would get the exact same result...a saw wave.
I know, and though I haven't tried this I assume I'd hear the sine waves in the audio range (even if the fundamental is below). So why can't I hear the same harmonics with a sawtooth in a subtractive analog or VA?
#5
2nd February 2013
Old 2nd February 2013
  #5
just ask audioinsult...
#6
2nd February 2013
Old 2nd February 2013
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may i facepalm?? pleeeease

first.. do that with a strong lab oscilator and you will realize that your stupid pluginDA combo just dont has what it takes to deliver low end energy..
because when the fundamental is weak allready the harmonics will be even lower.But thats only a a tad more beefy. Your speaker cant do 10hz..so it wont create the harmonic on the 10hz waveform too.. what you hear is the windnoises and 10 hz clicks.

So in case you have a speaker that goes below 20hz and a DA that does or analog generator.. You will have the harmonics and the low end energy will be brutal.. a friend has 30 inchwoovers.. they are scary..thats not clicking anymore..thats subs
#7
2nd February 2013
Old 2nd February 2013
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you can't be serious...
#8
2nd February 2013
Old 2nd February 2013
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this has to do with the gammtone filtering of human hearing
other as commonly assumed the ear is sensitive to phase,
or rather: to phase alignment
in hearing, time and frequency have critical resolution

here you see an example of a gammatone filterbank output:
http://www.southampton.ac.uk/aim/aim-figures/bmms.jpg

you clearly see the onsets of the waveshape
these are processed by the brain in a correlation like fashion,
where the correlation gives (part of) the pitch impression

when the phases are not aligned, and the frequencies are slightly drifting
it sounds very different (for these low pitches you mention)

just send your low pitched sound through a long and dense reverb
to note the difference

in addition, pitch is perceived by the spacing between harmonics,
(though you cant seperate that property from the time correlation)
so even if the fundamental is missing you perceive the same pitch
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Gil missFlag
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2nd February 2013
Old 2nd February 2013
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Originally Posted by memristor View Post
this has to do with the gammtone filtering of human hearing
other as commonly assumed the ear is sensitive to phase,
or rather: to phase alignment
in hearing, time and frequency have critical resolution

here you see an example of a gammatone filterbank output:
http://www.southampton.ac.uk/aim/aim-figures/bmms.jpg

you clearly see the onsets of the waveshape
these are processed by the brain in a correlation like fashion,
where the correlation gives (part of) the pitch impression

when the phases are not aligned, and the frequencies are slightly drifting
it sounds very different (for these low pitches you mention)

just send your low pitched sound through a long and dense reverb
to note the difference

in addition, pitch is perceived by the spacing between harmonics,
(though you cant seperate that property from the time correlation)
so even if the fundamental is missing you perceive the same pitch
Great explanation, thanks!
So what you're basically saying is that if I were to alter the phase of some of those harmonics, my ears would be able to hear them? It's the fact that they are locked in phase with the fundamental that makes them inaudible?

BTW to "mister facepalm" up there, I tried the same thing with analog oscillators and no AD conversion, and I know my speaker can't produce 10hz - but I was asking why I can't hear 50,60,70hz and above.
#10
2nd February 2013
Old 2nd February 2013
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Quote:
Originally Posted by Gil missFlag View Post
Great explanation, thanks!
So what you're basically saying is that if I were to alter the phase of some of those harmonics, my ears would be able to hear them? It's the fact that they are locked in phase with the fundamental that makes them inaudible?

BTW to "mister facepalm" up there, I tried the same thing with analog oscillators and no AD conversion, and I know my speaker can't produce 10hz - but I was asking why I can't hear 50,60,70hz and above.
come on..dont act stubborn

The 10 hz are not produced by the speaker therefore the harmonics on it dont get produced...

this is a mechanical process and not an informational one.. so leave the phase alone or i call the linear phase smurf.

a speaker is producing the waveform..not its partials... when its not mechanical able to transfer that waveform into acoustical energy the harmonics just dont happen. the membrane moves with 10 hz and not in all frequencys at once.. ok.. it does to a certain degree..thats the clicks...but after the transient there is no energy or air moovement agaib..

comprendre?

we live in a physical world !
#11
2nd February 2013
Old 2nd February 2013
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What if you filter out the fundamental and turn up the harmonics?
#12
2nd February 2013
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Quote:
Originally Posted by Sotsirc View Post
What if you filter out the fundamental and turn up the harmonics?
when this happens in a range the speaker can produce you have the harmonics up..

try with a 100 hz saw wave..

problem with 10 hz is that its ridicolous low.. you really need something like the 30 inch woofers of my friend to get this working in audible ways..
#13
2nd February 2013
Old 2nd February 2013
  #13
Quote:
Originally Posted by audioconsult View Post
The 10 hz are not produced by the speaker therefore the harmonics on it dont get produced...
interesting...so why can i hear a 50hz saw wave on my tiny earbuds which definately can not produce the fundamental...?
Gil missFlag
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#14
2nd February 2013
Old 2nd February 2013
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Originally Posted by audioconsult View Post
come on..dont act stubborn

The 10 hz are not produced by the speaker therefore the harmonics on it dont get produced...

this is a mechanical process and not an informational one.. so leave the phase alone or i call the linear phase smurf.

a speaker is producing the waveform..not its partials... when its not mechanical able to transfer that waveform into acoustical energy the harmonics just dont happen. the membrane moves with 10 hz and not in all frequencys at once.. ok.. it does to a certain degree..thats the clicks...but after the transient there is no energy or air moovement agaib..

comprendre?

we live in a physical world !
I realize that. However, ultimately any mix of oscillators or different sounds is summed into one waveform (or two if stereo). If I add a 10hz sine to my mix, I'm still going to hear all the other frequencies in the summed waveform even though the speakers can't reproduce 10hz, right? So I was expecting the same from a plain sawtooth or square wave.
#15
2nd February 2013
Old 2nd February 2013
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Quote:
Originally Posted by Gil missFlag View Post
I realize that. However, ultimately any mix of oscillators or different sounds is summed into one waveform (or two if stereo). If I add a 10hz sine to my mix, I'm still going to hear all the other frequencies in the summed waveform even though the speakers can't reproduce 10hz, right? So I was expecting the same from a plain sawtooth or square wave.
but the mix stays together.. you cant just remove one of the frequencys without effecting all the others..

so when the mechanical lowcut of the speaker itself is applied on the mix, the resulting waveform is not a 10hz saw anymore.. so the levels of the 2nd. 4th and 8th partia ( 20,40 and 80 hz)l are not relative to the original mix, the 10 hz saw.. they relate to the result of a 10hz saw send thru a heavy low cut.... and thats dependend on the lowcut way lower partial levels than you would have got when the speaker would be able to produce lower frequencies. Normal smaller monitors would do maybe the 6th partial at the correct level.. but as the waveformthey give to the air is no Saw anymore the 6th partials, 60hz, level is lowered..

in the end you have your harmonics ..thats the clicks..all the highest harmonics are there and mask the too low level lower harmonics..

As i ve said.-. the monster bass speakers of my friend with a resonance freq at 15 hz sound evil on 10 hz lfo┬┤s..thats allmost dangerous for the structure of the house.
As soon your speaker can do it your harmonics sound like a bass and not just like clicks.
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