Topic: I managed to overload my FR-AV2 mini-jack mic input with a pair of Clippy mics

[TheJez]

Just to share my experience...
Earlier this year I got a Tascam FR-AV2 and a pair of Clippy microphones (EM272M capsules) with 3.5mm mini-jack connector. The main goal was to get less-noisier recordings for more quiet shows than I was able to create previously with an Edirol R09HR with a pair of Core Sound Stealth Cardioids.
I was very pleased with the result, regarding getting rid of noise as well as the richness of the sound. I was very impressed with the sound of the Clippies v.s. their price.
Next up: A loud rock show! Because I was pleased with the result of the more quiet recording, I wanted to give the Clippies a chance. As I knew these were less suited for very loud music, I knew there would be a risk. But how loud is 'very loud'? It is not 'Extremely loud', right? 'Just to make sure to be able to deal with the high SPL, I built my own 9V battery box to power the mics. (Just in case the 5V PIP of the Tascam wouldn't be enough.)
I was standing about 2m (~7ft) from a filler speaker at the side of the stage, 'record level' to 0dB so I would see the real levels of what comes out of the ADC's on the VU meters without any digital amplification. Very soon into the first song, I noticed that the VU-bars on the recorder were completely red, which means that the analog input is overloaded. The bars still went back and forth a bit, though, so not constantly pushed to their max. Anyway, not good :-(. I had to move away from the PA quite a bit to make the VU bars color 'normal'. Unfortunately, there I picked up far more crowd noise than I wished for, so all in all it turned out to be one of my worst recordings ever.
Back home, I decided to do some math (which I could have and should have done before instead of after the show), with some help of AI, as I'm not very good at that and always find the dBV's, dBU's, Pa's and whatever very confusing...:
- The Clippies / EM272 have a sensitivity of ~40mV/Pa
- Max SPL of the EM272 is ~122dB
- Max input of mini-jack mic input of the FRAV2 is +1 dBV, which is apparently ~ 1.122V
With 40mV/Pa sensitivy, we would need about 123 dB SPL to get a voltage of 1.122V. So apparently I had to deal with a SPL of more than 123 dB as the analog input was overloaded! To be honest, this surprises me. I was thinking that the SPL at the show was lower. Yes, it was loud (especially near the speaker), but was it that loud?? Or did I miscalculate somewhere?
Anyway, I have been thinking of ways to deal with this better in the future, e.g.:
- Use/build an attenuator of e.g. -6dB or -10dB), so I can make sure that the output of the mics won't overload the analog input?
- Build a 3.5mm-to-2xXLR connector so I can connect my (unbalanced) Clippy mics to the XLR inputs? Not sure if this as such would help, though, as the max input of the XLR input (when configured as mic-in) is +4 dBU, which is apparently 0.975 V, which is lower than the 1.122V of the mini-jack input! (). Or maybe set to line-in, so the max input would be +24V, which is apparently 12.3V, which would be way too high for the Clippy mics.
And, regardless, apparently loud concerts can easily reach the max SPL of the mics themselves anyway, so whatever tricks done after the mics will not prevent the distortion by the mics themselves.
So the bottom-line is that I just need some less sensitive mics for loud shows. I may revert to the Core Sound's or try to get some other mics.
Maybe someone more math-savy can double-check my observations and conclusions. Any comment is welcome.
Otherwise I just put this here to share my experience, so others won't make the same mistake as I did...

[Joop]

I was standing about 2m (~7ft) from a filler speaker at the side of the stage, 'record level' to 0dB so I would see the real levels of what comes out of the ADC's on the VU meters without any digital amplification. Very soon into the first song, I noticed that the VU-bars on the recorder were completely red, which means that the analog input is overloaded.

This is the first strange thing in reading. Why set record level to 0dB? In your case -20dB would do perfectly.

Yes, it was loud (especially near the speaker), but was it that loud?? Or did I miscalculate somewhere?

Yes,unfortunately lots of stage folks still think that loud is some kind of quality. It is not, next; how about your ears? That kind of volume is good for only about 1.5 second per day listening before damaging your ears! (based on 80dBspl 8hours, 3dB up half that time).

There is almost no difference between XLR or 3.5mm with mic use, except that XLR is phantom power and 3.5mm does have PIP. So your calculation is wrong. The maximum input on XLR is +4dBu and that is 1.227652988V (site Sengpielaudio), so its a little more than max. 3.5mm input. Setting things to line will switch off phantom power or PIP,  because there are not such equipment which need that.

Clipping is still possible, the marker is the +4dBu which seems to pop up in every spec with double ADC's. Yes, it is possible to overload the input with the Clippy's.

So start with a record level of -20dB (-18dB (Default) recommended in the manual), the noise floor is sufficient low for getting that in the way.

[datbrad]

The FR-AV2 manual lists the max signal for the 1/8" unbalanced input to be +1 dBV, so you definitely need a lower sensitivity microphone. You might want to consider the DPA 4099s, they are only 6 mv/PA, and I think they have a version coming out soon that is only 2 mv/PA.

[TheJez]

This is the first strange thing in reading. Why set record level to 0dB? In your case -20dB would do perfectly.
...
So start with a record level of -20dB (-18dB (Default) recommended in the manual), the noise floor is sufficient low for getting that in the way.

Thank you Joop for responding. I guess I should have made myself more clear. The analog gain stage is fixed with the FR-AV2 (as with most 32bfp recorders). All you can do is apply some digital amplification after the A/D conversion to get the volume of the recorded samples within a desired range (e.g. around -12dB or whatever). In case of the FR-AV2, you can set the post-adc digital amplification (confusingly indicated as 'Record Level' in the manual and on the device) between a value of 0dB (=no amplification) to +60dB (much amplification). I was trying to say that I set the digital amplification AKA 'Record Level' to 0dB. In such a situation, the VU-bars will show what comes out of the A/D conversion without any digital amplification. I did this to get a sense of how far away I would be from clipping the analog stage, assuming that the analog clipping point would be on or just below the ADC clipping point.

Yes, it is possible to overload the input with the Clippy's.

Yes, and this happens sooner than I was expecting. Found it out the hard way... Lesson learned!

[TheJez]

The FR-AV2 manual lists the max signal for the 1/8" unbalanced input to be +1 dBV, so you definitely need a lower sensitivity microphone. You might want to consider the DPA 4099s, they are only 6 mv/PA, and I think they have a version coming out soon that is only 2 mv/PA.

Thanks for the suggestion. I defenately need mics with a lower sensitivity for the louder stuff! I fear DPA's are out of my financial reach, yet I consider SP-CMC-4 or 8, either with low sensitivity patch (~5mV/Pa) or with XLR's. They need to be stealthable...

[VibrationOfLife]

I've made a ton of recordings with clippies.  You are overloading the mics, not the recorder.  You can't do that to those mics, period.  Move them to a quieter area, stack on some some wind pro.  They aren't meant for what you are using them for.

[TheJez]

I've made a ton of recordings with clippies.  You are overloading the mics, not the recorder.  You can't do that to those mics, period.  Move them to a quieter area, stack on some some wind pro.  They aren't meant for what you are using them for.

I was defenately overloading the recorder. It nicely indicates this by making all segments of the VU-bars completely red (instead of the normal green->red segments)
I expect that I may have been also overloading the mics. One doesn't rule out the other. When I moved back from the speakers, the overloading (recorder and/or mic) was gone, but I got much more crowd noise than I was aiming for.
I made very nice recordings too with the Clippies, but these were quieter performances. I wanted to know its limits, and now I found them 

[TheJez]

Maybe for those interested, I've attached a picture of a piece of the waveform during the overload. It is what was recorded (32bfp), without any post-processing.
Some remarks:
- The waveform isn't clipped flat/rock-solid to 0dB. It looks to me there is some analog clipping going on, which was confirmed by the recorder showing the 'analog input overload indication'.
- Remarkably, the waveform at the bottom shows samples louder than 0dB! I wasn't expecting that, given the fact that the 'record-level'/digital magnification was set to 0dB. Even with dual ADC, I never would have thought to see that without digital amplification. (Also no equalization or other effects are applied in the recorder) Could it be the switching between the two ADC's is too slow in this situation?? I'd be surprised of the 'ADC for more quiet sounds' would be engaged here at all...

[VibrationOfLife]

You fundamentally do not understand what has been posted.

[grawk]

If you overload the front end, the adc can’t fix it. Period.

[TheJez]

You fundamentally do not understand what has been posted.

Hm, ok... Maybe you can explain what it is that I don't understand?

[TheJez]

If you overload the front end, the adc can’t fix it. Period.

I know! I never expected it would. I was a) just trying to make clear that is was indeed the front end of the recorder that was overloaded (in response to VibrationOfLife who said I was not overloading the front end, just the mics), and b) that even though I am aware that the front end was overloaded, I am still a bit surprised about what was actually being recorded (i.e. sample values > 0dB, while no digital gain was applied)

[grawk]

Going over 0db is a feature of 32bit float.  If there is distortion before then from overloading the mics or the preamp, it'll record it, and you can listen, you get to avoid "digital over".  Analog distortion isn't as painful to listen to generally, it used to be the goal of the designs.

[TheJez]

Going over 0db is a feature of 32bit float.

I am aware that being able to go over 0dB is a feature of the format. I was expecting that samples > 0dB could only happen when the 'record level' is set to something bigger than 0dB, which it often is.
Let me try to explain what I mean:
No matter the analog input (overloaded or not), when the output of the lowest sensitivy ADC (= the one taking care of loud input, so to say) is at its max (0dBFS), how could there be samples stored > 0dB? I'd say that can only happen if there is some form of post-ADC amplification in the digital domain going on. As I set the so called 'record level' to 0dB, I was expecting no digital amplification at all, hence expecting no samples > 0dB.
The only explanation I can think of is that there is some digital amplification going on anyway, and one can set some 'extra amplification' by means of the 'record level'.

[grawk]

That's the disconnect.  The 32bit float container can store data well above 0db.  You can demonstrate this by simply plugging in a line level source, set the preamp to 0db, and turn up the volume on the source until you're hitting above 0db.  Then load it into a DAW, and normalize it to -0.5db, and you'll see the dynamics return.