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Gear / Technical Help => Microphones & Setup => Topic started by: icebox on June 02, 2014, 01:55:32 AM
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I recorded a show tonight, using CA-14 omnis plugged into a CA-9200 plugged into the line input on a Sony M-10. The 9200 was set with volume at about 50%, and 35db gain. (I had thought this was set with 15db gain, but I misread the box). Volume in the club wasn't that loud. The M-10 had it's rec level at 4, and levels peaked at -9. When I set the levels, the green lights on the M-10 were flashing, which suggested to me levels around -10 to -12, and for the most part the levels are around -10 there. I was in a balcony about 10 feet from speakers, the mic setup was on the floor, with the mics attached to the front of a camera bag and with the mics about 6" above the floor positioned so they would be at the level of the long horizontal gap between the balcony railing and the floor. M10 and 9200 were inside the bag.
When I got home and started listening to what I had, there are many places that have distortion, looks to be around 50-60 hz. The voice distorts at points too. I didn't hear any distortion in the club, so that's not what I was picking up. What did I do wrong? How do I have distortion when the levels never go anywhere near 0?
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Were the batteries in the CA-9200 fresh and/or fully charged? Not sure if the 35dB gain has something to do with it or not, but it sounds like one hell of a lot of gain for amplified music. I would check the batteries first.
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Including this show, this is the 4th show that I've used the 9200, and the device was turned off immediately after each use. I'm not sure how long the batteries should last, and I don't have a tester handy. But if the batteries were low, why would that cause peak distortion at normal levels? As for the gain, I was surprised when I checked the box before posting and saw where it had been set. I wonder if that was the reason as well.
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If your batteries were low they would not be powering the mics adequately and that could cause the mics to distort at high SPL. You would not register that mic distortion on the M10 and would only see normal levels as expected.
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wondering if you might have left the mics plugged into the preamp between shows? This is a constant low battery drain on some battery boxes and maybe on your preamp, too. ??? I agree, this sounds like a low battery situation
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What would be the purpose of having an attenuator following the gain control? So would best practice be to run the 9200 with the volume maxed, control the gain only with the gain knob and dial the volume back only if it was too hot for your recorder (or just attenuate using the recorder if possible)?
I think the problem is the gain and only the gain. I believe in Chris' amp, the volume control is an attenuator that follows the gain control. If you clip the amp with the gain control, the volume control can't fix that. So you get an attenuated clipped signal, which you think is OK because the Sony sees a normal level, but it's still clipped.
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wondering if you might have left the mics plugged into the preamp between shows? This is a constant low battery drain on some battery boxes and maybe on your preamp, too. ??? I agree, this sounds like a low battery situation
the mics were not plugged into the preamp between shows. I disconnect everything afterwards. The batteries have about 7 hours of use. I thought I had a battery tester, but I can't find it. Haven't really had need for one for about 5 or more years. I'll get one tomorrow if I can't find mine here. That will let us get clear evidence on this theory.
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I think the problem is the gain and only the gain. I believe in Chris' amp, the volume control is an attenuator that follows the gain control. If you clip the amp with the gain control, the volume control can't fix that. So you get an attenuated clipped signal, which you think is OK because the Sony sees a normal level, but it's still clipped.
Zoom in on your waveform: opamps will hard clip symmetrically--you'll have flat tops and bottoms, whereas the FET in the mic will soft clip asymmetrically--only one side will be flat, and it will be a smoothish kind of flat. If it's the former, the problem was your gain setting.
I've attached a screenshot of a closeup of two peaks in a distorted section. Is this clipping? The long straight lines make me wonder, although nothing is flat.
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Thanks Jon. So nice to discover the properties of the equipment by screwing up an otherwise perfect setup; great location, and mic placement that eliminated close audience noise. Really frustrating. Chris, if you see this, it'd be nice to have a manual with the battery box so we know about these things. With stealth recording, there's really no way to know if the battery box is putting out garbage until it's too late. Maybe a trouble light on the box is warranted. I figured since the levels were OK on the device, any combination of settings on the battery box would be OK. And now I have learned, but have a useless recording to go along with it. A million ways to screw up a recording even when you think you know what you're doing. Sigh.