Topic: Binaural setup results in mono recording. What could cause this?

[edmaddict]

- Standing front row, a couple feet left of center
- In a large enclosed dome (NBA arena)
- Loud bass heavy  Electronic Dance Music
- Possibly related post from 2014 (in which the cause is not revealed) http://taperssection.com/index.php?topic=168357.msg2094531;topicseen#msg2094531
- Batteries were brand new (voltage of every cell checked before recording)

Gear chain used:
(2) DPA 4061 (on glasses) -> CA Ugly2 with microdot connectors -> Core Sound 20db Attenuator (TRS) -> Personally made patch cable (Mogami 2697) (TRS) -> (Line In) Sony PCM M10

Will provide information, just not sure what else I might include.

[dabbler]

Start by reproducing the problem at home; just snap your fingers or tap your mics.
Then eliminate extra pieces you don't need, such as the attenuator cable to isolate the problem.
Perhaps try going into mic-in instead of line-in on the M10, too.

If your DPAs were stereo mini-plug terminated, you could bypass the Ugly2 and use the mic-in PiP for low-level testing.
The M10 PiP can power the 4061s for quiet recordings, at least.

You can also try recording something else into line-in/mic-in or builtin-mics
of the M10 to eliminate the M10 itself as a failure point.

[edmaddict]

dabbler,

Thank you for writing up the troubleshooting advice.

Set everything back up, as of yet no repro    I'll spend some more time trying to repro. I had all the connections taped, doesn't seem like that would _hurt_ anything, but I've learned to check my assumptions.

[edmaddict]

Called my dad. "Sounds like a short between the tip and ring". Bingo.

My money is on the attenuator, I've had nothing but trouble with it. Will be building my own.

I hope this helps someone else if you encounter this problem.

Thank you

[edmaddict]

Bingo, opened the center portion of the attenuator and found it can easily short between any combination of left/right/ground.

Off to find attenuator plans.

[dabbler]

Good to know you've figured it out!  Taking a step back, do you need an attenuator at all instead of dialing back levels on the Ugly2 and M10?
In my experience: fewer parts, fewer problems

I don't even use a preamp, just DPA 4061 > battery box[1] > M10 line-in anywhere
from level 4 and above.

[1] http://taperssection.com/index.php?topic=80917.msg1080069#msg1080069

[Gutbucket]

Was going to guess a short between signal conductors, via a problem in a cable, the attenuator, one of the terminations, or via a not fully inserted plug, each of which could cause that.

You may be able to completely eliminate the attenuator.   


The trick is setting up good gain-staging.  You have three points of variable gain adjustment in the recording chain: the input level of the M10 is one of those and the CA-UGLY2 provides two additional separate gain adjustments.  The CA-UGLY2 is capable of something like +40dB of gain, yet you will not need much gain from it at all.  For very loud bass-heavy music, you will mostly be using it to power the mics and buffer the signal without much gain change. 

Here's how to do so:

Assuming this kind of material the loudest stuff you record, first set the M10 to a comfortable setting for a hot input (I don't use an M10 so I can't suggest what an appropriate low number is on that machine - but set it a little above whatever it's lowest safe input setting is to allow you some range of fine-adjustment). 

Then dial in the appropriate gains on the CA-UGLY2 to get the levels about where you want them. By first setting the rotary gain switch on the CA-UGLY to its lowest level (fully counter-clockwise).  Then adjust the two small trim potentiometers with a small screwdriver, there is one for each channel.  Adjust them so that the loudest music you will record is peaking where you want it on the M10 meter.  Adjust the fine-balance between the two channels using the same trim pots to make them as close as possible.

From there you can make fine gain adjustments via the M10 while recording.  And you can make larger, gross-level base-line adjustments by turning the rotary switch on the UGLY2 clockwise to it's higher gain settings as necessary for recording less-loud music.  Once properly adjusted you shouldn't need to adjust the trim-pots further.  Note: The trim pots should end up somewhere in the middle of their adjustment range, if you can only get good levels with them turned almost completely counter-clockwise (without much range left before they mute) then you will need attenuation between the UGLY and M10.

[edmaddict]

Thanks Gutbucket and dabble,

Do I need the attenuator?  GREAT question.

When using a 20db attenuator:
- Ugly at 0 gain
- M10 at 5-6

I never thought of adjusting UGLY's the potentiometers.

Didn't know there was a range I should stay within the for M10, I'll dig that out of the boards.

I can't reproduce these sound levels, but I can probably approximate them.

It's great to get feedback from fellow tapers. Haven't met one in person yet.

[Gutbucket]

The two trim potentiometers are primarily for balancing the two channels.  With the trims turned fully clockwise (which is their default setting if you've never adjusted them), the gain through the preamp equals whatever the rotary switch is set to.  As you turn each trim counter-clockwise, gain is reduced from the setting of the rotary switch in that channel.  Turned fully counter-clockwise, the gain attenuation is infinite (the channel mutes).  So in addition to allowing fine-adjustment of gain balance for two microphones with slightly different sensitivities, you can also use them to reduce the gain through both channels by an equal amount.  The reduction applied via the trimmers applies to all positions of the rotary gain switch.  When the trims are adjusted together - turned down by the same relative amount - they reduce the gain through the preamp below the nominal settings of the main rotary gain switch- from full gain of that switch position (fully clockwise), down to mute (fully counter-clockwise).

It is best to to have the trims set closer to the middle of their range or higher if possible, and not too far counter-clockwise.

------------------

Most small recorders have a certain point on their input level adjustment which you should always remain above, when adjusting input gain to achieve good recording levels.  At input level settings lower than that (for louder material) the input stage of the recorder overloads and distort before the signal gets to the metering point.  When that happens the meters on the recorder will not show any overload, and often the clip indicator light, if the recorder provides one, will not indicate clipping, however the signal is already distorted by the time it has reached the meters.

That's referred to around here as "brickwalling" because the waveform flattens out at that signal level when viewed in a audio editor, as if it had hit a brick-wall.  It is avoided by never setting the gain on the recorder lower than that "don't go below" input gain setting.  If you need to set the input gain lower and cannot do so some other way such as reducing gain through the preamp, then you need to use an attenuator between the preamp and recorder which will allow you to set the recorder's input levels above the "don't go below" point without clipping.

[fmaderjr]

Most small recorders have a certain point on their input level adjustment which you should always remain above, when adjusting input gain to achieve good recording levels.  At input level settings lower than that (for louder material) the input stage of the recorder overloads and distort before the signal gets to the metering point.  When that happens the meters on the recorder will not show any overload, and often the clip indicator light, if the recorder provides one, will not indicate clipping, however the signal is already distorted by the time it has reached the meters.

This setting on the M10 is quite low (lower than any other hand held that I know of). Even at record level 1 (of 10) you will not brick wall if the levels stay under 0 dB. The level where you can bick wall without the meters indicating it on the M10 is a hair below level 1, I think.