Hi, I'm using a subwoofer as a microphone for low frequencies on a didgeridoo and find that it seems to pitch shift everything slightly downward. I've read about adding a pad switch, and that it is important that impedances match, and the possibility of using a DI box. But all this is in the context of how it is a hot, unbalanced signal, prone to distortion and feedback, etc. Nothing I have read tells me why this pitch shift might be happening. I am hoping someone here might have a good explanation.
I do understand that every mic (or speaker used as a mic) is going to have a different frequency response curve. I also understand that the subjective perception of pitch is colored by the relative loudnesses of the various harmonics that make for timbre. So, perhaps my perception of pitch shift is just an illusion based on the different cones and their respective frequency response curves, but it really seems too pronounced to be just this. I've compared the sub-mic (a 4 or 5 inch Genesis subwoofer) to a Sennheiser e906 mic, and the sub-mic seems about a 1/4 tone lower in pitch.
So I'm asking, would the fact that the impedance of the sub-as-mic likely does not match the input impedance on my pre-amp be responsible for pitch shifting the signal? Is there another potential explanation? Any way to correct it (other than finding a different speaker)?
I do understand that every mic (or speaker used as a mic) is going to have a different frequency response curve. I also understand that the subjective perception of pitch is colored by the relative loudnesses of the various harmonics that make for timbre. So, perhaps my perception of pitch shift is just an illusion based on the different cones and their respective frequency response curves, but it really seems too pronounced to be just this. I've compared the sub-mic (a 4 or 5 inch Genesis subwoofer) to a Sennheiser e906 mic, and the sub-mic seems about a 1/4 tone lower in pitch.
So I'm asking, would the fact that the impedance of the sub-as-mic likely does not match the input impedance on my pre-amp be responsible for pitch shifting the signal? Is there another potential explanation? Any way to correct it (other than finding a different speaker)?
"Complicated electronics is required to "Pitch Shift". The sub will give more lower register than upper but cannot shift the pitch on its own, whatever the impedance mismatch or whatever."
That's what I am inclined to think.
"Yamaha Music use a 4" bass speaker as a kick drum mic and it works very well!"
Now why would I waste my money on that?! I'm sure it works great, but it would be a $400 waste when less than $50 and some time will get the same results--or better from some of the reviews I read.
That's what I am inclined to think.
"Yamaha Music use a 4" bass speaker as a kick drum mic and it works very well!"
Now why would I waste my money on that?! I'm sure it works great, but it would be a $400 waste when less than $50 and some time will get the same results--or better from some of the reviews I read.
I don't think it is necessary to use a subwoofer for that purpose in the first place ! A smaller driver like they use with the aforementioned Yamaha mic would take up your didgeridoo as well IMO.
Regarding phase shift: Did you ever try to connect a resistor with very few ohms accross the subs terminals ? You may probably excite the subs fs and perceive the ringing on fs as pitch-shift. If you load it then you will dampen the resonance. But this comes at the cost of lower output voltage.
Regards
Charles
Regarding phase shift: Did you ever try to connect a resistor with very few ohms accross the subs terminals ? You may probably excite the subs fs and perceive the ringing on fs as pitch-shift. If you load it then you will dampen the resonance. But this comes at the cost of lower output voltage.
Regards
Charles
The aforementioned Yamaha mic IS a subwoofer. See SKRM-100SFV - Subkick - Acoustic Drum Accessories - Drums - Musical Instruments - Products - Yamaha United States
And it is 6.5", not 4". (Unless there is another Yamaha subwoofer mic I haven't heard about)
I have experimented with a variety of mics vs. subwoofers, and no small diaphragm mic can capture the low end like a subwoofer. Not even with the added bass effect of placing the mic right up in the bell end of the instrument. And not with fancy EQ either. But I'm not here to defend my experiment-backed point that, no, you can't get as impressive results with a small diaphragm. I am here to ask for advice regarding the pitch shift issue...
No, I have not connected a resistor or anything like that. I'm not sure I understand: "You may probably excite the subs fs and perceive the ringing on fs as pitch-shift."
And it is 6.5", not 4". (Unless there is another Yamaha subwoofer mic I haven't heard about)
I have experimented with a variety of mics vs. subwoofers, and no small diaphragm mic can capture the low end like a subwoofer. Not even with the added bass effect of placing the mic right up in the bell end of the instrument. And not with fancy EQ either. But I'm not here to defend my experiment-backed point that, no, you can't get as impressive results with a small diaphragm. I am here to ask for advice regarding the pitch shift issue...
No, I have not connected a resistor or anything like that. I'm not sure I understand: "You may probably excite the subs fs and perceive the ringing on fs as pitch-shift."
Do you have access to a spectrum analyzer or osciloscoop with FFT math? if it really is a pitch shift it should show up in the frequency domain, if you use a sine wave as input signal and compare it to the signal from the woofer they should overlap if there is no pitch shift. If there is a pitch shift probably some sidebands are generated (AM modulation)
Intermodulation distortion can cause sum and difference frequencies to appear in a signal. Perhaps you are hearing the IM difference signal instead of the fundamental as your "frequency shift".
I worked on a thunder recording project in 1972, where we used commercial microphones that were specified to be flat 100 to 1/3 hz. They had about a 2" diaphragm.
I worked on a thunder recording project in 1972, where we used commercial microphones that were specified to be flat 100 to 1/3 hz. They had about a 2" diaphragm.
Yes, sidebands and sum and difference frequencies are two different names for the same phenomenon. See Intermodulation - Wikipedia, the free encyclopedia
If your speaker as microphone is non-linear (and there is no reason to think it is not, linearity costs money and a lot of testing to achieve) then a sine wave going in comes out as the fundamental frequency plus other frequencies. There may be more than one frequency generated, in fact a whole range of them.
If your speaker as microphone is non-linear (and there is no reason to think it is not, linearity costs money and a lot of testing to achieve) then a sine wave going in comes out as the fundamental frequency plus other frequencies. There may be more than one frequency generated, in fact a whole range of them.
Hey Guys,
I wonder if this is a case of "missing fundamentals" (google it) if there are non-linearites in the pickup system generating harmonics......??
Its used in stuff like this : MaxxBass - Bass Enhancer Plugin | Waves
I wonder if this is a case of "missing fundamentals" (google it) if there are non-linearites in the pickup system generating harmonics......??
Its used in stuff like this : MaxxBass - Bass Enhancer Plugin | Waves
There is no way for the signal to shift in frequency without some non-linear behavior, this non-linear behavior shows up in the frequency domain as sidebands (which are sum and difference signals of the original signal + the distortion signal). Where this distortion maybe coming from is something to be investigated if this hypothesis is confirmed. But to give an example, if the (primary) sidebands are 50 or 100Hz (60 - 120Hz in the US) from the fundamental I would take a good hard look at my (linear) power supply.
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Maybe the math will help clear things up, this is the basic formula for AM modulation (see attachment). taken from this Wikipedia page: http://en.wikipedia.org/wiki/Amplitude_modulation
This may also be helpful: http://en.wikipedia.org/wiki/Sideband
This may also be helpful: http://en.wikipedia.org/wiki/Sideband
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Isolate the problem. I am reading here several interesting theories, but all are based upon assuming a certain cause. May I suggest some tests. Maybe they are not what you need, but perhaps might give you an idea.
Have the instrument played, and someone listens to the speakers of the PA system. Mic the instrument with your subwoofer and then mic with an actual microphone. Does the shift happen only with the subwoofer and not the regular mic? Does the listener hear any shift at all? As it could be the hearing of the player that is affected. And on that theme, if you hear the shift while playing, do you still hear it when someone else plays? Does it matter if you are listening to amplified sound live or from a recording?
Non-linearity was mentioned. The human ear is non-linear, so it is not automatic to ignore that. This may be of interest:
http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/pitch/pitch.html
I have often heard low notes that seem to shift as the volume gets high, working on systems in my pro audio shop here. It could be my ears, it could be my speakers, I doubt it is the electronics. That is a listening situation, but I see no reason to think it couldn't happen on the recording end.
Have the instrument played, and someone listens to the speakers of the PA system. Mic the instrument with your subwoofer and then mic with an actual microphone. Does the shift happen only with the subwoofer and not the regular mic? Does the listener hear any shift at all? As it could be the hearing of the player that is affected. And on that theme, if you hear the shift while playing, do you still hear it when someone else plays? Does it matter if you are listening to amplified sound live or from a recording?
Non-linearity was mentioned. The human ear is non-linear, so it is not automatic to ignore that. This may be of interest:
http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/pitch/pitch.html
I have often heard low notes that seem to shift as the volume gets high, working on systems in my pro audio shop here. It could be my ears, it could be my speakers, I doubt it is the electronics. That is a listening situation, but I see no reason to think it couldn't happen on the recording end.
The kick drum signal contains transients. These contain frequeny content below the fundamental "ringing" frequency. Remember diff eq? The solutions contain both a natural and forced response. That forced response is an impulse - do an FFT on that and see what comes up. The same is true of the sub driver itself. Hit it with a transient (ie, tap on the cone) and it rings at fs. The less damping the more it rings - short the terminals any you don't get much. So what you end up with is a hodge-podge of the kick's fundamental, harmonics, fs of the sub, and the IM products from all of them. It should sound "thicker", if you had to put a description to it. A real mic will have a low mass and very well damped resonance, to minimize such coloration.
I've always found that kick drums do not sound natural on a system that's not flat to the low 20's, especially a dry kick that doesn't have all the usual processing which doesn't sound "natural" anyway.
I've always found that kick drums do not sound natural on a system that's not flat to the low 20's, especially a dry kick that doesn't have all the usual processing which doesn't sound "natural" anyway.
yes its a little more than that. it has to do with harmonic response. About 20 years ago, when I started to experiment with different drivers as microphones, the speakers fs is directly related to even harmonic sensitivity. as the diaphragm gets bigger, the amount of even harmonics before Fourier attenuation is less.
"o" bridge attenuator 3:1 at 150 ohm. seems to work the best for me.
In my humble opinion, a speaker isn't sufficient as a standalone device for capturing audio, but it would do nicely when paired with a traditional microphone. I've seen this done using Yamaha NS10 speakers with an SM57 in a recording studio in Tennessee. Neither input sources sounded great independently, but together, it was pretty glorious.
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