Dayton IMM6-C microphone gain adjustment

[Fernando Moraes Brasil Santos]

Hi everyone, I was wondering if anyone could help me out.

I initially bought an IMM6 to align the sound system at my church.

However, after some time and research, I was told that measurements might not be very accurate in this case because the phone itself could be introducing frequency interference through the input jack.

I was then advised to buy an IMM6-C, which operates on the premise that the signal isn't processed by the phone's internal circuitry since it connects directly via USB-C.

So, I bought the microphone and started running some tests.

Indeed, the response curve of the IMM6-C isn't the same as that of the IMM6 (I know they wouldn't be identical, but I expected something closer, given that both come with calibration files).

I ran several tests and noticed that the IMM6-C microphone was causing input clipping (saturation).

I discovered this because I own a calibrated sound level calibrator; when I apply a 94dB signal, the IMM6 calibrates perfectly without clipping. However, when I use the IMM6-C, the AudioTool input clips—indicated by a red warning—which doesn't happen with the IMM6.

I suspect there might be some sort of digital gain or similar process occurring with the IMM6-C.

To verify this, I connected the IMM6-C to a laptop, and the clipping occurred in the same way. However, I went into the Windows settings and lowered the microphone sensitivity from 100 to 47; the level became perfect, with no clipping at all. In fact, I even switched the calibrator from 94dB to 114dB, and the result was spot-on.

I’d like to know if there is any way to control the IMM6-C's gain within AudioTool.

[Julian Bunn]

Hi Fernando,

You could try applying a Global Offset via the Menu to bring the level to what it should be?

Julian

[Fernando Moraes Brasil Santos]

Yes, using the CAL-5000—a professional sound level calibrator—I obtained an offset of -18; however, the issue is that the audio input is clipping.

Example using the IMM6:

- I set the calibrator to 94 dB.
- I insert the microphone into the calibrator.
- AudioTool shows 89.8 dB.
- I adjust the offset to +4.2 (IMM6 offset).
- AudioTool shows exactly 94 dB.
- I switch the calibrator to 114 dB.
- AudioTool shows exactly 114 dB.
(Neither shows clipping or a red signal.)

Example with the IMM6-C:

- I set the calibrator to 94 dB.
- I insert the microphone into the calibrator.
- AudioTool shows 112 dB.
- I adjust the offset to -18 (IMM6-C offset).
- AudioTool shows exactly 94 dB, but it is clipping (everything turns red).
- I switch the calibrator to 114 dB.
- AudioTool shows 95.6 dB, clipping in the same way.

I know the problem isn't with my IMM6-C, because I tested it the same way by connecting it to a laptop, and it works perfectly—without saturation or clipping.

I’m not sure if it would be possible to include a method for controlling the microphone input gain.

It’s done in USB-C recording apps like USB Audio Recorder, for instance; that app allows me to select the input gain level.

I also don't know if this is handled directly on the USB device or if it is actually being applied within Android.

[Julian Bunn]

Hi Fernando,

Thanks for the detailed description! AudioTool is using the 16 bit mono PCM sample stream from the microphone, whatever microphone is connected. This stream is provided by the Android OS. If any incoming sample is greater than 95% of the maximum possible value of a 16 bit short, then the "clip" flag is turned on and the display turns red. 

It seems that in the case of the iMM6C there is some pre-amplification being applied somewhere before AudioTool receives the sample stream from the device. 

It's a bit odd, and I need to investigate further.

Julian

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[Ian Eales]

Try Google Sound Amplifier app 

- Ian

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[Fernando Moraes Brasil Santos]

Good afternoon, my friend. I tested this app.

I tried various parameters, but nothing I adjust makes any difference in AudioTool.

[pa sk]

Hello,

Have you tried this mike with some other analyser/recorder app on your phone?

"Hi-Res Audio Recorder" is an excellent audio recorder in which you can choose audio "source" from several available;

You cannot explicitly choose the mike you use, and IMO a "source" means the processing (method) applied by Android to the input signal.

Although you cannot see the input wave - it's neither a scope or RTA - but you can record the sample and then analyse it in e.g. Audacity;

Another app could be Spectroid but in this case you have the spectrum only (with waterfall if needed), so you cannot see the clipping right away but you can look for "side effects" clipping gives in f domain, e.g. if you apply sine wave, what you in fact do using calibrator, you'll get spectrum with plethora of harmonics which would be absent if there was no clipping.

Regards

[pa sk]

forgot to add: Hi-Res Audio Recorder has also the function of applying amplification/attenuation to what is recorded

regards

[Fernando Moraes Brasil Santos]

I have USB Audio Recorder, and it does indeed have attenuation and volume control buttons.

The problem is that the settings applied in this app don't carry over to AudioTool.

It’s as if the parameters reset to default every time I open the app.

[pa sk]

Hello Fernando!

And how's your "fight"? Did you find some workaround/solution?

Regards,

Paweł S.