Topic: Bottom Half of Waveform Clipping

[VibrationOfLife]

Thank you so much for saving me more hours that I've already put in swapping mics and cables and power supplies.  You folks are a gem, and that is why I posted in this subforum.  You can pull your hair out trying to track this **** down.

al.w dm me your paypal so I can gladly buy you a beer.

[Gordon]

something is off!  first is in iZotope rx 11, second is wavelab Pro 12

[VibrationOfLife]

More heart attacks.  Any clues?

What I do know for a fact is there is no clipping on the absolute scale.  My limiters never touched on the input or the output of the 422 and the Tascam never came close to anything above -8 dB.  But the sound files don't lie, unless they do.  Also, I'm simultaneously recording the SBD.  And recording to 32 bit float, so that rules out the recorder.  And the waveforms are mostly symmetrical on a DIN setup.  Rrrrg.

The haircut mystery continues.  This is so weird and this is why I'm going nuts.

We have so much real crap to deal with in our lives, so I really appreciate all of you taking the time to try to solve this with me.  I really really appreciate this little niche of our caring.

It also just occurred to me that we bring a lot of crap to shows.  Most people would think that is a mess, but I find it logical and soothing.

[EmRR]

Very interesting mystery.

al w.'s Logic screen capture is perfectly symmetrical, like Logic is doing a phase rotation in the graphics.  Usually things aren't THAT symmetrical.  If I do a phase rotation in the 60-120 degree range I get something much more symmetrical. 

All the other screen captures look like light clipping, and I generally would find it a toss-up as to whether that would be audible or not, it really depends on the source. 

In RX11 if I toss everything under 45Hz it starts looking less clipped.  There's a bunch of energy centered on 40Hz, kick drum.  Even more symmetrical at 55Hz.  A -3dB shelf EQ at 100Hz does similar things.   As does a 40Hz -6dB notch at a Q of 1.  You can still see the flatline across the transients, but it's not as obvious.   FWIW. 

It could be kick and bass with brick wall limiting coming out of subs with limiting, generating an acoustic signal that looks flat lined on one side.  That would be surprising, but maybe.   Mics placed in a room node that's acoustically maxing out? 

Single ended power supplies (like phantom, or class A single ended tubes) tend to clip asymmetrically, it could be the mic asking for more current than is possible on low freq transients, or the recorder supply similarly not keeping up for whatever reason. 

If I push the output control on my Tascam 122mkIII cassette deck with a hot tape, it generates similar waveforms, which don't necessarily have any obvious artifacts.  It's one of the things I look for when setting up a transfer. 

If it sounds good, it is good!  but can it be better.....?   

Going back into pre-history with radio broadcast rules, it was legal to be a certain % past 100% to the postive, but not a bit over on the negative, so there were broadcast limiters that you could set to do exactly that, and they would flip polarity if the other side of the waveform gave greater legal output.  If you limit drums with one of those set to 125% positive, they do seem to shoot out of the speakers more than if set for 100%. 

Interested to learn what the fix turns out to be. 

[VibrationOfLife]

I'm completely at a loss at this point because when I try to recreate it at home I can't, but certain decency limits me to certain SPL's.  This is the first time it has shown up in both channels.  It's annoying.

Does it affect the end result, no.  Does it make me want to pull my hair out, yes.  I've narrowed it down to the preamp.   I'll call sound devices and see if they still can do a check over/cla on it as there are some leds that are out.  Will probably cost me more than the unit, but the security is worth paying for in my book.  Hell, I still shoot multiple film cameras from the 1950's that I maintain religiously, including all the lenses.

I've just never seen that before.  Bottom haircut mystery remains.  I'll update if they actually are willing to look at it.  It's pretty old, but there might be a chance?

[daspyknows]

Go test stuff out at a bar with a shitty cover band.  Experiment with what you can think of and track the changes.  I have resorted to that to try and test gear.

[VibrationOfLife]

I did that last night.  I nailed my perfect gain in from the mics, separated the sbd feed, and now I'm down to what I got.  Which is great, but it's not right.  I don't need a dive bar to tell me how my stuff is working or not, but I appreciate the idea. I happened to be able to tape in a perfect acoustical space where I could set up mics and get a board feed.  Thanks, FOH and the band.   I spent 4 hours yesterday beforehand trying to duplicate it, which I couldn't, then I hit some serious SPL in a taping environment and it showed up again.  The pull is fantastic, but the waveform is Fubard.  I'll keep working on the reason.  It's an old preamp mixer, a SD 442, into a digital world.  The gain and the faders are super sensitive, but from my headphones monitoring the music, it is pristine from both the pre and the recorder.  Within a half dB.  But the files are fucddd.  That is why I don't know what to do.  Maybe I can call and send it in for a tuneup.  I don't really need it, I can run straight into my recorder with good old USA 48v phantom power, but I do notice a difference in the quality, slightly, when I run my mics through the 442.  If I didn't, I wouldn't bother carrying the big brick.  I could run with something out of my pocket.

[VibrationOfLife]

Go test stuff out at a bar with a shitty cover band.  Experiment with what you can think of and track the changes.  I have resorted to that to try and test gear.

https://archive.org/details/trg2025-12-02

[morst]

Go test stuff out at a bar with a shitty cover band.  Experiment with what you can think of and track the changes.  I have resorted to that to try and test gear.

https://archive.org/details/trg2025-12-02

I'm really curious where that file actually goes.  If I knew, if there was some transparency, I'd be very inclined to upload files to it.  But I don't see that happening because, from my own experience, the place is run like shit, given that it does barely its job.  I'd like to improve it, but I have absolutely zero trust in that institution.  Maybe if they actually did more than a PR piece every couple of years, or maybe if they answered a single e-mail.  But otherwise, they can sink or swim.

[grawk]

RX shows no problems with the first file, so I'm comfortable writing it off as a rendering bug on your software

[Gutbucket]

Just came across this thread.  My first thought was that the waveform looked like what I've experienced from power starvation in a single ended supply preamp. But display of the full waveform upon zoom in and in other software seems to indicate some sort of 32bit float waveform display issue.  The data appears to be there (stronger evidence), with no obvious distortion upon listening (corroborating if weaker evidence).

I suspect either the 32-bit recorder writing the file info or a software rendering bug as grawk mentions.

Couple troubleshooting things you might try in the same situation which caused the issue (sufficiently high SPL):
1) Same mics > direct in (or different preamp) > same recorder set to record 32-bit float as before.
2) Same mics > same preamp > same recorder, except set to record to 24 bit rather than 32-float.
^
The first is a check of the preamp.
The second is a check of the recorder's 32bit mode.

The following things also came to mind. +T as they are quite insightful regarding asymmetrical clipping.. if it were actually clipped.

It could be kick and bass with brick wall limiting coming out of subs with limiting, generating an acoustic signal that looks flat lined on one side.  That would be surprising, but maybe.   Mics placed in a room node that's acoustically maxing out? 

Single ended power supplies (like phantom, or class A single ended tubes) tend to clip asymmetrically, it could be the mic asking for more current than is possible on low freq transients, or the recorder supply similarly not keeping up for whatever reason.

[..snip..]
 
Going back into pre-history with radio broadcast rules, it was legal to be a certain % past 100% to the postive, but not a bit over on the negative, so there were broadcast limiters that you could set to do exactly that, and they would flip polarity if the other side of the waveform gave greater legal output.  If you limit drums with one of those set to 125% positive, they do seem to shoot out of the speakers more than if set for 100%.

[goodcooker]

FWIW I never had any issues out of that preamp before I parted ways with it. I didn't use it a lot in the last few years - which is why I sold it - but I used it as recently as last Jazzfest to mix the broadcast signal for the live stream at Bayou Rendezvous.

I ran it from an Anker 5V USB battery with the Hirose cable that I included in the sale. Never any powering issues but maybe try a higher output battery if yours is on the low end. If using phantom power double check the switches on the input side. One mic getting P48 and the other getting 12V could screw things up but still appear to work fine on the meters. The official DC power supply outputs 2A @ 12V.

Double check all of the locking switches on the front. The low cut filters are on a rotary switch - that clicks out to adjust then recesses to lock - to the right of each channel fader on the front. Maybe one of those got moved somehow?

There's also a "hidden" menu (that they call the Setup Menu) of features outlined in the manual that uses the LED peak meters and a series of front panel button pushes to configure. Maybe something got inadvertently changed in there. Most of those adjustments are not probably relevant to your issue (it's mostly stuff like meter ballistics and configuring the 10pin) but hitting the factory default may help. There's a couple of settings for a few of the outputs in there.

Here's a list of the outputs and their impedance. You may have an impedance mismatch to the inputs of your recorder which can cause a low cut to happen. Not sure what that recorder is I see sitting on top of your bag. A Tascam X8? If it's a mismatch maybe try using a different output or using the configuration switches (or Setup Menu for the TA3 outs to configure) rather than the direct outs on the other side. The XLR main outs are transformer balanced - both the TA3 direct and main outs are impedance balanced - and this matters if you are using consumer type gear downstream. I typically only used the direct outs via the TA3 cables I supplied with it at sale and I used it with a few different recorders mostly a Tascam DR701d, also a "prosumer" deck. Just throwing out ideas.

XLR Line: Transformer-balanced for use with >600 ohm inputs
XLR -10: Transformer-balanced for use with >10k ohm inputs
XLR Mic: Transformer-balanced for use with >600 ohm inputs
Multipin Line: Transformer-balanced for use with >600 ohm inputs
Multipin -10: Transformer-balanced for use with >10k ohm inputs
Multipin Mic: Transformer-balanced for use with >600 ohm inputs
TA3 Balanced Mic and Line: Impedance-balanced, pin-2 driven, for use with >3k ohm inputs
TA3 Direct Outs Mic and Line: Impedance-balanced, pin-2 driven, for use with >3k ohm inputs
Tape Outs (3.5 mm and TA3-type): Unbalanced, stereo, for use with >6k ohm inputs
Mono Mic Out: Unbalanced, mono, for use with >600 ohm inputs
Headphones (3.5 mm and 1/4"): Unbalanced, stereo, for use with 8-2k ohm headphones

[VibrationOfLife]

I'm going to try 2 things different tonight: 1) use a separate power supply for the pre and the recorder, and 2) instead of using the TA3 balanced L + R out, I'm going to use the direct pre fader outs for each channel.

We'll see if I can repeat it with this config.  The only change I made in the setup menu was to adjust the meter ballistics +4dB.  When phantom power is supplied to the inputs it's all or nothing, 12v or 48v to all of them.   I'm giving clean 48v.

[VibrationOfLife]

Better, but I'm still not liking the waveforms.  It's all there.  I probably would need to throw down $800 for Sound Devices to do a full look-over, but the pulls are good enough for me.

https://archive.org/details/moontricks-12052025-flac-24  Still seeing the "clipping" on the audience mics, but when I normalize them and mix them, they sound great to me.  So I'll save my coin for tickets, not wickets.

[EmRR]

CM-4's, yes?  They draw a little more power than many things, but not on the high end of things.  Other than a power thing, I don't see a possible problem with those.

Sound Devices, looking at the manual, not fully grasping the power situation.  Are the various settings purely related to the power metering, or are they settings for various types of external power sources?   The fact that it's a mixer, possible to drive the input trims too hot and the master too low.  Interesting that it looks like a VCA mix bus. 

I'd sure test direct in to the recorder with the mics.  Do a mono run through the Sound Devices with only one mic instead of 2.   Run one mic through the Sound Devices, and the other direct to the recorder.