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need technical audio help (Read 300 times)

Offline andhow04

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need technical audio help
« on: October 27, 2020, 01:51:26 PM »
i have been using the Zoom H6 as an external mic for the ipad pro. it works really well. last night i recorded a lot of music, over an hour.. the second half was schubert impromptus op 90.

unfortunately there is a popping sound going through all the impromptus which i did not realize until this morning

the other music i recorded, does not have that.

in between that music and the schubert i changed the batteries on the zoom. so something didn't work out right, and i am not sure what it is. here is one of them on youtube, you can hear the popping right away-



Offline quantum

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Re: need technical audio help
«Reply #1 on: October 27, 2020, 05:34:15 PM »
Can you do further tests?  Try to replicate the results.  Setup your gear just like in your recording session, and include the battery change. 

Try recording only with the H6 as a standalone device.  Include a battery change. 

Record with the iPad alone, using the app you utilized in your session.

Swap cables to a known good one between the iPad and H6, test.

Was your iPad installing updates during the recording, or using any of the antennas for active transfer of data?

Try a complete reboot of both the iPad an the H6.  For the H6 remove the batteries for one minute (it might erase your settings and time, so be prepared for that). 

I've heard similar on one of my interfaces before.   The solution was to not touch certain buttons while recording. 

If you upload an mp3, we can have close look at the wavform inside an editor to see what those pops really look like. 

Made a Liszt. Need new Handel's for Soler panel & Alkan foil. Will Faure Stein on the way to pick up Mendels' sohn. Josquin get Wolfgangs Schu with Clara. Gone Chopin, I'll be Bach

Offline andhow04

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Re: need technical audio help
«Reply #2 on: October 27, 2020, 10:35:32 PM »
thanks for your great response. i was unable to try the zoom again today but i will do that tomorrow. reading through i suspect one thing though, and that is, this time i turned trhe ipad to "Do not disturb" rather than "Airplane" mode. i was on wifi so yes it was probably active during the time of the recording...

hwoever that said i will try all the components seperately. thanks so much

Offline perfect_pitch

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Re: need technical audio help
«Reply #3 on: October 28, 2020, 10:33:59 AM »
unfortunately there is a popping sound going through all the impromptus which i did not realize until this morning

Do you hear the Pops only in louder more sudden parts of the music? It could be you are overloading the microphone 'preamp' I believe it's called. Sometimes the Zooms will tell you if you have recorded louder than the -0db limit.

Offline quantum

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Re: need technical audio help
«Reply #4 on: October 28, 2020, 12:58:20 PM »
Do you hear the Pops only in louder more sudden parts of the music? It could be you are overloading the microphone 'preamp' I believe it's called. Sometimes the Zooms will tell you if you have recorded louder than the -0db limit.

An examination of the wavform would reveal if this is the culprit.  If surrounding waves near the transient clips are near 0dB it might lead in that direction.  However, if the average peak of the wavform is well clear of 0dB, and the music is not necessarily at its loudest volume, then there might be other causes. 

One way of avoiding clipping is to record using 32 bit floating point, making use of its headroom.  It is rather useful in live recordings where there might not be an opportunity to do retakes.  That said, it is not an excuse to avoid doing due diligence and checking audio levels beforehand. 

Made a Liszt. Need new Handel's for Soler panel & Alkan foil. Will Faure Stein on the way to pick up Mendels' sohn. Josquin get Wolfgangs Schu with Clara. Gone Chopin, I'll be Bach

Offline perfect_pitch

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Re: need technical audio help
«Reply #5 on: October 28, 2020, 02:09:56 PM »
That said, it is not an excuse to avoid doing due diligence and checking audio levels beforehand. 

That seems a little harsh... there's a learning curve to doing your own recording and I found that out the hard way, but I guess it is important, as not doing it can wreck a very good recording session.

Also, some of the newer Zoom H models allow you to record 2 streams simultaneously - one at normal levels, and one at -6dB which means if your primary recording is too loud, then the other one will hopefully have less pops and crackles (since it's softer and hopefully didn't overload the sensor)

It took me a while to tweak it, but with my setup - the microphone is always at the same position each time. All I did was take 5 pages of the loudest music, play it and continually decrease the volume level until I no longer over-peaked the microphone.

Online j_tour

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Re: need technical audio help
«Reply #6 on: October 28, 2020, 07:50:00 PM »
That seems a little harsh... there's a learning curve to doing your own recording and I found that out the hard way, but I guess it is important, as not doing it can wreck a very good recording session.

I wouldn't go that far.  I didn't know, for example, that the hardware representation of real numbers acted as, essentially, a wider tape, if what quantum said is right.  Not padding the input with impedance, but giving a wider canvas.  More or less.

And you yourself gave me a bit to look into with the various late-model Zooms coming out:  that's kind of a neat isolation booth capability built in, I suppose.  I wonder how much storage space and HW details, but, I'm not recording anybody now.

It seems like everyone agrees:  check your levels.  Duh, there's a reason it's called a sound check.  But I learned a couple of safety catches in the case one doesn't have a familiarity with the room or what sound is like. 

I therefore deem this thread informative.
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Offline quantum

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Re: need technical audio help
«Reply #7 on: October 29, 2020, 08:22:21 AM »
One way of avoiding clipping is to record using 32 bit floating point, making use of its headroom.  It is rather useful in live recordings where there might not be an opportunity to do retakes.  That said, it is not an excuse to avoid doing due diligence and checking audio levels beforehand. 

That seems a little harsh... there's a learning curve to doing your own recording and I found that out the hard way, but I guess it is important, as not doing it can wreck a very good recording session.

I was referring to recording using 32 bit floating point, in which it is not an unrecoverable disaster to have peaks higher than 0dB.  There is less worry about peaks above 0dB as one can recover by simply attenuating the wav, the data is still there you just have to adjust the file.  In comparison, fixed point bitrates one cannot record data higher than 0dB. 

To put things  in perspective here are some dynamic ranges you could expect from common bit rates:
16 bit fixed point: 96.3 dB
24 bit fixed point: 144.5 dB
32 bit floating point: 1528 dB

For 32 bit floating point the noise floor is -758 dB and the max value is 770 dB. 

Speaking pragmatically, 32 bit floating point provides a range far beyond what would be reasonably required to capture musical sounds within a digital file.  It allows a more flexible post production workflow because you can adjust the file in post, to either boost quiet sounds or attenuate ones that go over 0 dB.  It is much more forgiving in live recordings when you have the possibility of unexpected peaks, or unknown sound levels from sources. 

That said, good recording technique is always good practice.  One should not become lazy just because the technology allows it.  With fixed point bit rates, one should absolutely check levels before recording, it is an essential requirement. 

Placing the dynamic range of recorded sounds correctly was one of the first things I learned when starting recording.  The results of not doing this can be disastrous and frustrating to the music being recorded.  Out of experience, I quickly learned the importance of understanding this.

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Back to the OP, I am leaning towards the problem not being clips as a result of gain being set too high.  If you listen to the first few seconds, the attack of the opening chord does not produce a pop, yet there are small pops during the much quieter sustain portion of the chord.  There are bigger pops during the single note melody, again much softer in volume than the opening chord, very unlikely caused by clips due to high gain. 
Made a Liszt. Need new Handel's for Soler panel & Alkan foil. Will Faure Stein on the way to pick up Mendels' sohn. Josquin get Wolfgangs Schu with Clara. Gone Chopin, I'll be Bach

Offline ronde_des_sylphes

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Re: need technical audio help
«Reply #8 on: October 29, 2020, 09:22:06 AM »
I'm having a similar problem, albeit with pops caused during attempted streaming.

It categorically is NOT clipping. I've captured a bit of the audio from the performance by the OP and put it into iZotope: here is a screenshot. The audacity capture file isn't close to clipping at any point.