<p>Tessa Rinehart writes in her AudioMoth guide
<a href="https://github.com/rhine3/audiomoth-guide/blob/master/guide.md#create-configuration" rel="nofollow noreferrer">https://github.com/rhine3/audiomoth-guide/blob/master/guide.md#create-configuration</a></p>
<blockquote>
<p>The gain is the amount that sounds from the microphone will be
amplified once recorded. <strong>Selecting the optimal gain requires trial and
error in your particular field conditions</strong>. If the gain is too high,
your recordings will clip, creating an unpleasant distortion that can
be challenging, if not impossible, to analyze. Alternatively, if the
gain is too low, sounds will be faint and hard to hear.</p>
</blockquote>
<p>(emphasis added)</p>
<p>My own conclusion: AudioMoth invites you for experimentation and learning by making errors.</p>
<p><strong>Edit</strong>:
Concerning the gain settings
<a href="https://www.openacousticdevices.info/support/main/comment/60800bbcbb7c0c001500dc98" rel="nofollow noreferrer">https://www.openacousticdevices.info/support/main/comment/60800bbcbb7c0c001500dc98</a>
gives the following gain values for 1.1.0:
[4.33, 7, 15, 25.1, 30].</p>
<p>These values are consitent with Sam's measurement (excluding top two values, where saturation/nonlinearity may play a role).</p>
<p><strong>Edit2</strong>: After checking with the EFM32WG reference manual (the processor used in AudioMoth) It turns ot that the gain values should be linear and would result to the followng dB values [12.7, 16.9, 23.5, 28.0, 29,5]. Subtracting these dB values from the observed values of [{-99.5, -95.4, -89.2, -84.6, -82.2] on obtains [-112.2, -112.3, -112.7, -112.6, -111.7], which is at least roughly constant pretty much -18dBV/Pa (Mic sensitivity) minus 94 dB.</p>

CC BY-SA 4.0
2024-05-02T12:48:32.320Z
Maybe I wasn't specific enough. I would like to know the amplification gain that the op-amps in the AudioMoth are "adding". In combination with microphone sensibility (which I know), it should be possible to estimate sound pressure levels. I do know the "best" gain settings for my use case.
Dominik
CC BY-SA 4.0
2024-05-06T07:14:42.707Z
added info from openacousticdevices
WMXZ
CC BY-SA 4.0
2024-05-06T11:29:29.127Z
Thanks for the update. That's what I was looking for.
Dominik
CC BY-SA 4.0
2024-05-07T12:58:29.210Z
Interestingly, adding up the gain does not match the empirically observed gain well, unless my calculations are wrong:
Sam Lapp
CC BY-SA 4.0
2024-05-07T13:06:59.430Z
(sorry accidentally hit enter)
maximum voltage amplitude = 3.3/2= 1.65 corresponds to 3.01 dBFS |
so 1V signal: -1.34 dBFS |
1 Pa acoustic signal = 94 dB SPL |
sensitivity Med gain = -18 + 15 = -3 dBV/Pa |
so 1Pa becomes -3 dBV = -4.34 dBFS after gain |
end-to-end dB SPL - dBFS = 98.3 dB  |
(observed: 89 dB) |
Sam Lapp
CC BY-SA 4.0
2024-05-08T14:40:46.013Z
@Sam, it seems the numbers are linear and taking the log values make your observations more in-line. Edited my answer.
WMXZ
CC BY-SA 4.0
2024-05-02T12:17:41.543Z
2024-09-05T10:50:57.487Z
2024-09-05T10:50:57.487Z
WMXZ
<p>Estimating the end-to-end sensitivity of a microphone and recording system can be done (A) by knowing each component's gain and frequency response or (B) &quot;empirically&quot; end-to-end.  Note that Audiomoth configuration allows 5 gain settings. (A) is hard because I don't know the pre-amp gain and I'm not sure it's published anywhere (also note that the hardware components and the way the gain is implemented in hardware have changed over AudioMoth versions). I'm sure Alex Rogers from Open Acoustics Devices would be able to answer for a specific version and setting.</p>
<p>On the other hand, (B) is easy. I have measured the end-to-end sensitivity (i.e., calibrating digital dBFS to dB SPL) empirically. I found the offset from the real-world dBA of a pink noise signal  to the A-weighted digital signal's DBFS to be the following for each of 5 gain settings:
{0: -99.5,
1: -95.4,
2: -89.2,
3: -84.6,
4: -82.2}
Don't take these measurements as exact though: these measurements did not use anechoic chambers or professional standardized coupling (pistonphone) and may not be very accurate. Also, ARUs decrease in sensitivity over a multi-year lifespan (<a href="https://pdfs.semanticscholar.org/8d23/6f5f3db0bc0f5a94b1123c806562da5ff5b2.pdf" rel="noreferrer">https://pdfs.semanticscholar.org/8d23/6f5f3db0bc0f5a94b1123c806562da5ff5b2.pdf</a>).</p>
<p>My recommendation is to empirically measure a few of your recorders' sensitivity: play pink noise at a level that does not clip the recording; measure dBA at the recorder with an SPL meter; apply A weighting to the digital signal then calculate dBFS; calculate the difference between dBFS and dBA.</p>
<p>I'll note that the Audiomoth (and any ARU) is not equally sensitive across frequencies, or in all directions, and that these two factors interact. This is especially true when adding a protective housing (so...always?). We've published a paper and online resource with additional frequency response measurements for axes of rotation, and for various housings:
<a href="https://www.mdpi.com/1424-8220/23/11/5254" rel="noreferrer">https://www.mdpi.com/1424-8220/23/11/5254</a>
<a href="https://github.com/kitzeslab/audiomoth-performance" rel="noreferrer">https://github.com/kitzeslab/audiomoth-performance</a></p>
<p>Hope this is helpful!</p>

CC BY-SA 4.0
2024-05-06T11:28:50.280Z
Thanks a lot! this helps.
Dominik
CC BY-SA 4.0
2024-07-21T10:53:25.713Z
@Dominik If it's a good answer, please could you "Accept" it (click on the big "tick-mark") - that helps to give credit in the right places
Dan Stowell
CC BY-SA 4.0
2024-05-05T02:00:37.190Z
2024-05-05T02:00:37.190Z
Sam Lapp
<p>For a while now, I have been trying to find specifications for the amplification gain of <a href="https://www.openacousticdevices.info/audiomoth" rel="nofollow noreferrer">AudioMoth</a>.</p>
<p>As for the SM4 for example, one can find the exact dB declarations. If anyone can point me to that for the different AudioMoth configurations, that would be great.</p>
<p>These specifications would help by estimating sound pressure level for example.</p>

CC BY-SA 4.0
2024-05-02T12:39:09.860Z
Would you like to estimate the **absolute** sound level from the specifications of a given Audiomoth and the amplitude of the recorded signal?
Noil
CC BY-SA 4.0
2024-05-02T12:46:22.713Z
Yes, that is what I think I am aiming for. For example, the Scikit-MAAD package allows for such things, if you know the actual amplification gain and microphone e.g.: https://scikit-maad.github.io/_auto_examples/2_advanced/plot_sound_pressure_level.html#sphx-glr-auto-examples-2-advanced-plot-sound-pressure-level-py
Dominik
<pam><audiomoth>
Amplification gain of AudioMoth
# Amplification gain of AudioMoth

(Asked by: username_0 on 2024-05-02)

For a while now, I have been trying to find specifications for the amplification gain of [AudioMoth](https://www.openacousticdevices.info/audiomoth).

As for the SM4 for example, one can find the exact dB declarations. If anyone can point me to that for the different AudioMoth configurations, that would be great.

These specifications would help by estimating sound pressure level for example.

**Tags:** pam, audiomoth

> **Comments:**
> **username_1**: Would you like to estimate the **absolute** sound level from the specifications of a given Audiomoth and the amplitude of the recorded signal?  
> **username_0**: Yes, that is what I think I am aiming for. For example, the Scikit-MAAD package allows for such things, if you know the actual amplification gain and microphone e.g.: https://scikit-maad.github.io/_auto_examples/2_advanced/plot_sound_pressure_level.html#sphx-glr-auto-examples-2-advanced-plot-sound-pressure-level-py  

---

## 2 answers

### Answer by username_3 on 2024-05-05. Score: 11 | Accepted answer

Estimating the end-to-end sensitivity of a microphone and recording system can be done (A) by knowing each component's gain and frequency response or (B) "empirically" end-to-end. Note that Audiomoth configuration allows 5 gain settings. (A) is hard because I don't know the pre-amp gain and I'm not sure it's published anywhere (also note that the hardware components and the way the gain is implemented in hardware have changed over AudioMoth versions). I'm sure Alex Rogers from Open Acoustics Devices would be able to answer for a specific version and setting.

On the other hand, (B) is easy. I have measured the end-to-end sensitivity (i.e., calibrating digital dBFS to dB SPL) empirically. I found the offset from the real-world dBA of a pink noise signal to the A-weighted digital signal's DBFS to be the following for each of 5 gain settings:
{0: -99.5,
1: -95.4,
2: -89.2,
3: -84.6,
4: -82.2}
Don't take these measurements as exact though: these measurements did not use anechoic chambers or professional standardized coupling (pistonphone) and may not be very accurate. Also, ARUs decrease in sensitivity over a multi-year lifespan (<https://pdfs.semanticscholar.org/8d23/6f5f3db0bc0f5a94b1123c806562da5ff5b2.pdf>).

My recommendation is to empirically measure a few of your recorders' sensitivity: play pink noise at a level that does not clip the recording; measure dBA at the recorder with an SPL meter; apply A weighting to the digital signal then calculate dBFS; calculate the difference between dBFS and dBA.

I'll note that the Audiomoth (and any ARU) is not equally sensitive across frequencies, or in all directions, and that these two factors interact. This is especially true when adding a protective housing (so...always?). We've published a paper and online resource with additional frequency response measurements for axes of rotation, and for various housings:
<https://www.mdpi.com/1424-8220/23/11/5254>
<https://github.com/kitzeslab/audiomoth-performance>

Hope this is helpful!

> **Comments:**
> **username_0**: Thanks a lot! this helps.  
> **username_4**: @username_0 If it's a good answer, please could you "Accept" it (click on the big "tick-mark") - that helps to give credit in the right places  

---

### Answer by username_2 on 2024-05-02. Score: 3

Tessa Rinehart writes in her AudioMoth guide
<https://github.com/rhine3/audiomoth-guide/blob/master/guide.md#create-configuration>

> The gain is the amount that sounds from the microphone will be
> amplified once recorded. **Selecting the optimal gain requires trial and
> error in your particular field conditions**. If the gain is too high,
> your recordings will clip, creating an unpleasant distortion that can
> be challenging, if not impossible, to analyze. Alternatively, if the
> gain is too low, sounds will be faint and hard to hear.

(emphasis added)

My own conclusion: AudioMoth invites you for experimentation and learning by making errors.

**Edit**:
Concerning the gain settings
<https://www.openacousticdevices.info/support/main/comment/60800bbcbb7c0c001500dc98>
gives the following gain values for 1.1.0:
[4.33, 7, 15, 25.1, 30].

These values are consitent with Sam's measurement (excluding top two values, where saturation/nonlinearity may play a role).

**Edit2**: After checking with the EFM32WG reference manual (the processor used in AudioMoth) It turns ot that the gain values should be linear and would result to the followng dB values [12.7, 16.9, 23.5, 28.0, 29,5]. Subtracting these dB values from the observed values of [{-99.5, -95.4, -89.2, -84.6, -82.2] on obtains [-112.2, -112.3, -112.7, -112.6, -111.7], which is at least roughly constant pretty much -18dBV/Pa (Mic sensitivity) minus 94 dB.

> **Comments:**
> **username_0**: Maybe I wasn't specific enough. I would like to know the amplification gain that the op-amps in the AudioMoth are "adding". In combination with microphone sensibility (which I know), it should be possible to estimate sound pressure levels. I do know the "best" gain settings for my use case.  
> **username_2**: added info from openacousticdevices  
> **username_0**: Thanks for the update. That's what I was looking for.  
> **username_3**: Interestingly, adding up the gain does not match the empirically observed gain well, unless my calculations are wrong:  
> **username_3**: (sorry accidentally hit enter) maximum voltage amplitude = 3.3/2= 1.65 corresponds to 3.01 dBFS | so 1V signal: -1.34 dBFS | 1 Pa acoustic signal = 94 dB SPL | sensitivity Med gain = -18 + 15 = -3 dBV/Pa | so 1Pa becomes -3 dBV = -4.34 dBFS after gain | end-to-end dB SPL - dBFS = 98.3 dB  | (observed: 89 dB) |  
> **username_2**: @Sam, it seems the numbers are linear and taking the log values make your observations more in-line. Edited my answer.  

---

