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Re: Quirky Microphone Inharmonicity Measurements!
johnlewisgrant #2509108 02/10/16 02:42 PM
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I did my own stereo test. Using a H2n Zoom in X-Y mode, I recorded A4 and using 1.80secs of the recording (86,400 samples). I analysed the first two partials, one set using a Rife-Vinc 1 window and the other a Hamming window.

Rife-Vinc............Hamming
L440.2687...........440.2500
R440.2625...........440.2462

L881.5856...........881.5707
R881.3474...........881.3689

I used to think the doppler effect, especially in woofers, could be sensed, but I have not seen any literature supporting that claim, nor have I been able to detect a widening of partial peaks due to woofer cone movement.

As you say, Paul, it's the amplitude of the partials that is important. EPT converts the linear FFT bins to log bins with one cent widths, adding another layer of error.

Edit: For the fun of it, I tried another sample from the A4 stereo recording. It is precisely 1.000 seconds long, and yield the following measurements.

Highest bin........next highest bin(3db down)
L439.9999..........440.9999
R439.9999..........440.9999

Interesting, because the R439.999 is the same amplitude as the L440.9999. Also interesting is the fact that the discrepancy is precisely 1.0000Hz, the same as the sample length, which is, of course, what the uncertainty principle predicts. Therefore, which frequency is correct?

[Linked Image]

Last edited by prout; 02/10/16 03:15 PM.
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Re: Quirky Microphone Inharmonicity Measurements!
prout #2509115 02/10/16 03:01 PM
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Originally Posted by prout


I used to think the doppler effect, especially in woofers, could be sensed, but I have not seen any literature supporting that claim, nor have I been able to detect a widening of partial peaks due to woofer cone movement.

As you say, Paul, it's the amplitude of the partials that is important. EPT converts the linear FFT bins to log bins with one cent widths, adding another layer of error.



I was thinking more of the doppler effect on the sensing transducer, not the reproducing one. I doubt most woofers have much, if any, response above a few hundred Hz anyway - so any doppler shift wouldn't be seen as there's nothing to shift. Also, I presume any such distortion would also show up as intermodulation distortion (you'd get the same sum and difference frequencies that would spread the partials).

I still wonder how accurate measurements need to be, given the finite precision that tuners are capable of, though I suppose errors are cumulative - though if they are randomly distributed across a temperament octave, maybe they're not so important. As an engineer, knowing when "good enough" is good enough is part of the art smile

Paul.

Re: Quirky Microphone Inharmonicity Measurements!
johnlewisgrant #2509126 02/10/16 03:22 PM
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Given that the average just noticeable difference in two sequential pitches is >5cents, it is the 'quality' of the unisons, and the beating of the important intervals that matter. Both can vary by several cents and not be disturbing to most listeners.


Re: Quirky Microphone Inharmonicity Measurements!
johnlewisgrant #2509136 02/10/16 03:43 PM
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A bad analog microphone can do all sorts of nasty stuff, but it cannot shift pitch.

(Try it for yourself -- if you have only one microphone, you can use headphones in lieu of a bad specimen, though you may need to apply plenty of gain. If you record simultaneously with both microphones connected to the same ADC clock you will see the partial pitches present in both channels align perfectly.)

Re: Quirky Microphone Inharmonicity Measurements!
prout #2509138 02/10/16 03:54 PM
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Originally Posted by prout
Given that the average just noticeable difference in two sequential pitches is >5cents, it is the 'quality' of the unisons, and the beating of the important intervals that matter. Both can vary by several cents and not be disturbing to most listeners.



True, but some of us got down to the 0.3c range for sequential JND of pitch. For unisons, I think it depends on how audible the higher partials areas to what pitch difference is just discernible between strings (i.e. you have to be able to hear a beat before the sound extinguishes).

Paul.

Re: Quirky Microphone Inharmonicity Measurements!
timq #2509152 02/10/16 04:48 PM
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Originally Posted by timq
A bad analog microphone can do all sorts of nasty stuff, but it cannot shift pitch.

(Try it for yourself -- if you have only one microphone, you can use headphones in lieu of a bad specimen, though you may need to apply plenty of gain. If you record simultaneously with both microphones connected to the same ADC clock you will see the partial pitches present in both channels align perfectly.)


'Pitch' is not frequency, and frequency is not what microphones sense. A mic senses a continuously changing pressure on the diaphragm. We convert that time-based dynamic into a continuum we call the audio frequency spectrum, then we choose to measure a particular point on the spectrum and give it the name 'frequency'.

Our perception of pitch (I use pitch here as meaning a complex waveform such as a struck piano string, or a pipe organ) changes with amplitude. Larger amplitude sounds are perceived as higher in pitch. A pitch recorded by two mics, with different frequency response curves, when played back through a theoretically perfect audio transducer, may be perceived as different from one mic to the other due to the different partial amplitudes recorded by each mic.

With regard to 'frequency' re-read my posts above. I have provided evidence that the frequencies measured by two mics recorded simultaneously are not the same.

Edit: I must add that I agree that the mic does not likely change the periodicity of the waveform, but it does not accurately reproduce the pressure on the diaphragm. That is a basic tenet of physics - the observer (the mic) affects the observed (the waveform). The result is measurement error, in both frequency, phase, and amplitude.

Last edited by prout; 02/10/16 05:00 PM.
Re: Quirky Microphone Inharmonicity Measurements!
pyropaul #2509157 02/10/16 04:52 PM
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Originally Posted by pyropaul
Originally Posted by prout
Given that the average just noticeable difference in two sequential pitches is >5cents, it is the 'quality' of the unisons, and the beating of the important intervals that matter. Both can vary by several cents and not be disturbing to most listeners.



True, but some of us got down to the 0.3c range for sequential JND of pitch. For unisons, I think it depends on how audible the higher partials areas to what pitch difference is just discernible between strings (i.e. you have to be able to hear a beat before the sound extinguishes).

Paul.


That is where the 'quality' of the unison comes into play. Aurally, I try to adjust the unisons to produce a consistent and hopefully nice tone. There is a wide range of tone variability available in a non-beating unison.

Re: Quirky Microphone Inharmonicity Measurements!
prout #2509171 02/10/16 05:17 PM
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Originally Posted by prout
Our perception of pitch (I use pitch here as meaning a complex waveform such as a struck piano string, or a pipe organ) changes with amplitude. Larger amplitude sounds are perceived as higher in pitch.

Oooh, prout! Be careful there... Steven's Rule of Pitch Perception. It's not always higher. Depends on the F0 of the stimulus.


Chris Storch
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Re: Quirky Microphone Inharmonicity Measurements!
Chris Storch #2509177 02/10/16 05:28 PM
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Originally Posted by Chris Storch
Originally Posted by prout
Our perception of pitch (I use pitch here as meaning a complex waveform such as a struck piano string, or a pipe organ) changes with amplitude. Larger amplitude sounds are perceived as higher in pitch.

Oooh, prout! Be careful there... Steven's Rule of Pitch Perception. It's not always higher. Depends on the F0 of the stimulus.


Sorry, you are absolutely correct. I left out the other half of the rule. cry But, with the single exception of 2000.000000Hz, changing the volume changes the perceived pitch.

Re: Quirky Microphone Inharmonicity Measurements!
johnlewisgrant #2509184 02/10/16 05:38 PM
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I thought perceived pitch was lowered by increased amplitude?

See Pitch versus Amplitude

Paul.

Re: Quirky Microphone Inharmonicity Measurements!
pyropaul #2509189 02/10/16 05:46 PM
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Originally Posted by pyropaul
I thought perceived pitch was lowered by increased amplitude?

See Pitch versus Amplitude

Paul.


For pure sine waves, pitches below about 2000Hz were perceived in subjective testing as decreasing with increasing volume, and pitches above 2000hHz were perceived as increasing with increasing volume. Complex waveform pitches were perceived as either higher or lower with increasing volume, based on the relative amplitudes of the partials.

Edit: Here is the last sentence from the 'Pitch versus Amplitude" article - "A special remark is that winds and strings in an orchestra tend to raise their frequencies a few cents at loud passages, presumably to conserve pitch."

Winds, when they blow harder to get louder, tend to increase the pitch of the note, and strings, when they press harder with the bow, increase the tension on the string which raises the pitch. From my discussions with orchestral players, they do not do this intentionally, except, upon occasion, to match the bloody piano that was tuned 50 cents sharp in the high treble in a feeble attempt to get it to be heard in the back row.

Last edited by prout; 02/10/16 06:47 PM.
Re: Quirky Microphone Inharmonicity Measurements!
johnlewisgrant #2509260 02/10/16 09:41 PM
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Sorry prout, of course you're right about my poor choice of words, and the correct way to state it is "a microphone does not shift frequency".

Re: Quirky Microphone Inharmonicity Measurements!
timq #2509292 02/10/16 11:30 PM
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Originally Posted by timq
Sorry prout, of course you're right about my poor choice of words, and the correct way to state it is "a microphone does not shift frequency".


No problem. I'm having a good day when I only mis-speak 10 times.

Re: Quirky Microphone Inharmonicity Measurements!
prout #2509535 02/11/16 05:47 PM
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Originally Posted by prout
No problem. I'm having a good day when I only mis-speak 10 times.

Lucky you! I have to consider it a good day when I realise my mistakes to begin with, or at least someone else does and points them out to me. smile

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