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distorted while Rx and level on the recorder both are fine


jimmycat
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I had a shouting scene in the rain where I wired the shouting female talent with a Countryman B6(low-sensitivity, red band, servo wired) via a SMQV(level set to 5) to 411a(compatible mode: NA 400, +5dbu, line in to 788t w/ limiter off). While the 411a never showed overmodulation sign and the the meter on 788t never hit red, the shouting is obviously distorted. The only cause I deduced is that the B6 itself was overloaded. However, with the maximum SPL of 130db of a low-sens B6 on the talent's chest, it's hard to get my head around how the overload from the lav is possible. Is there any other factor in the chain that might've gone wrong? 

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I once had the Lectro TX set to NA Hybrid and the RX was set to NU Hybrid. It cause distortion really early. TX limiters didn't kick in and the RX level meter looked totally good. Confused the hell out of me. Karl at Lectro later confirmed this can happen. Possibility?

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19 minutes ago, Trey LaCroix said:

I once had the Lectro TX set to NA Hybrid and the RX was set to NU Hybrid. It cause distortion really early. TX limiters didn't kick in and the RX level meter looked totally good. Confused the hell out of me. Karl at Lectro later confirmed this can happen. Possibility?

Good clue, but OP said "411a(compatible mode: NA 400".

 

2 hours ago, codyman said:

Definitely the mic.  You said it was a rain scene.  Did moisture get anywhere need the mic?  Maybe at the connector?  I've had connectors shorting out before which have done all sorts of odd sounding things.

Yep, water can make things sound weird from the mic element being fully, or slightly covered by a drop. And/or electrical disturbances on the connector could be water getting into the cable connector side, but possibly in the Tx connector too.

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I use the same gear, and the red band B6s are prone to overloading / distorting / clipping at the mic.  It's maddening because the blue bands don't clip but are super noisy at regular talking levels.  Conversely, red band Sankens don't seem to have that pronounced noise floor, they just don't clip.

 

I had a scene with Tim Heidecker on a recent gig, and he was presenting to a big group of people from a stage.  We were allowed to place the mic exposed, yay!  But the damn red band clipped on the loudest shouts.  We had to rewire after the first take, used a COS-11, and had no further problems.  These days I only use the red band B6s when it's the only thing that'll work.  I did use a blue band B6 today for a 70s gas guzzler tailpipe and that sounded awesome.

 

DPAs also don't clip like red band B6s do.

 

Last thing - gain level of 5 on a red band for shouting is right about where I put em, often going down to 0.  I have no idea how folks are using a gain of 25 or 30 for shouting!  6060s are hotter than B6s or COSs so often regular dialog is set at 14 or so, which puts the prefade peaks right between -8 and 0.

 

Dan Izen

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@Izen Ears Dan, good to know I'm not alone. I also have blue-band B6s and red-band COS-11s and have had exactly the same experience with you. Like you said, the blue-band B6 just sounds terribly noisy for regular-levelled dialogues, which made it almost impossible to use in film productions. As for the red-band COS-11, I've never heard it overloading. I had a doc about a professional basketball team where I wired the coach with an exposed red-band COS-11 in those super loud basketball games all the season and never had an issue. I didn't go for the COS-11 for this scene just because I was worried about the rain. I think the best bet in this situation would've been 6061s, if budget allowed.

 

Thanks for sharing. I'll avoid red-band B6s for good. But I'm also wondering: isn't it cheating that Countryman claims the maximum SPL of red-band B6s is 130db when it's clipping so easily? 
 

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I was looking up some DPA specs today and found https://www.dpamicrophones.com/mic-university/how-to-properly-attach-a-dpa-microphone-to-a-wireless-transmitter

 

The quote below from that page reminded me of this discussion.  With Lectrosonics servo bias wiring providing typically 4v bias, the max SPL would be reduced from the 130dB spec to somewhere around 120-124dB.

 

And, from the diagrams, the early stages of  distortion at that bias voltage would not look like clipping either.

 

Quote

The bias voltage available in most transmitters is in the range of 5-7 volts. However, a few brands provide only 2-4 volts. DPA miniature microphones (lavaliers, headsets and instrument mics) need 5-10 volts to work correctly. One exception, however, is the low voltage version DPA 4063 which works down to 3 volts.
 

What happens if the voltage is too low?

As mentioned, the output signal depends on the supplied DC voltage. If it is too low, it may result in asymmetrical clipping of the audio signal above a certain level [see figure 4]. The result is distortion; the lower the DC voltage, the more distortion at increased levels.
If the available bias voltage is, say, 4 or even 3 volts, the microphone still works. But the acoustical input must be reduced and kept below a limit, lower than the usually specified max SPL; this is to avoid distortion. In practice, a low bias voltage (3-4 volts) means that the max input signal must be kept approximately 6-10 dB below the specified max value.

 

 

 

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44 minutes ago, Matthew Steel said:

I was looking up some DPA specs today and found https://www.dpamicrophones.com/mic-university/how-to-properly-attach-a-dpa-microphone-to-a-wireless-transmitter

 

The quote below from that page reminded me of this discussion.  With Lectrosonics servo bias wiring providing typically 4v bias, the max SPL would be reduced from the 130dB spec to somewhere around 120-124dB.

 

And, from the diagrams, the early stages of  distortion at that bias voltage would not look like clipping either.

 

 

 

 

It is actually a lot more complicated than a simple 3, 4,or 5 Volt level. The recommended 5 Volt spec is with a resistor of 4.8k as used in some popular wireless. The actual voltage at the DPA mic is only 1.5 Volts and that voltage is fairly well fixed by the DPA circuitry, a compound FET and bipolar transistor circuit.  The resultant current draw with that 4.8k resistor and 5 Volt setup is slightly less than 1 mA. The servo bias circuit on the Lectro units was chosen to maintain about 4 Volts across the more common single FET mics. Since the servo bias circuit is trying to maintain 4 Volts and the DPA mic is trying to maintain about 1.5 Volts, large, noisy, current arguments ensue. This is perfectly resolved with the recommended resistor value shown in our wiring recommendation. The full audio Voltage swing is available with that choice.

Why does DPA recommend 5 Volts? Because with the internal resistors in some transmitters, it requires 5 Volts to get the optimum current (700uA) to the DPA mic. In an imperfect world, when the user has to use lower voltages, the user could just substitute a lower value internal resistor to keep the current at 0.7 mA (700uA). The downside is you would need to be able to get to the internal transmitter resistor. However, it is rarely a problem, since the DPA mics are very tolerant of various current values.

Best Regards,

Larry Fisher

 

 

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  • 2 weeks later...
On 9/7/2022 at 2:21 PM, Izen Ears said:

I use the same gear, and the red band B6s are prone to overloading / distorting / clipping at the mic.  It's maddening because the blue bands don't clip but are super noisy at regular talking levels.  Conversely, red band Sankens don't seem to have that pronounced noise floor, they just don't clip.

 

I had a scene with Tim Heidecker on a recent gig, and he was presenting to a big group of people from a stage.  We were allowed to place the mic exposed, yay!  But the damn red band clipped on the loudest shouts.  We had to rewire after the first take, used a COS-11, and had no further problems.  These days I only use the red band B6s when it's the only thing that'll work.  I did use a blue band B6 today for a 70s gas guzzler tailpipe and that sounded awesome.

 

DPAs also don't clip like red band B6s do.

 

Last thing - gain level of 5 on a red band for shouting is right about where I put em, often going down to 0.  I have no idea how folks are using a gain of 25 or 30 for shouting!  6060s are hotter than B6s or COSs so often regular dialog is set at 14 or so, which puts the prefade peaks right between -8 and 0.

 

Dan Izen

This has been my experience as well.  I have used the B6s for years and have several types of sensitivity models.  I never had this problem until a couple years ago when I started working with a Director who likes to have people yelling on many of his spots.  I ran into this same issue with the B6s overloading and have slowly started switching to DPAs.  A friend let me barrow his DPAs on the next shoot and I did not have that issue when someone yells.  So I decided to buy a few DPAs for this purpose.

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