Setting gain for mic and line in on Sound Devices 302
 

Hello,

I'm noticing that I'm having to set gain on my 302 near full out for my boom mic (Rode NTG-2 held about two feet away from subject with the mixer receiving the mic cable mic-in) also for a wireless mic when the receiver is connected to the mixer line-in. Is this normal? Just seems kind of funny.

Thanks.

John

(Original comment deleted) Don't know about the mixer but it's OK to turn up the gains on an XH-A1 when using a SD 302:

http://www.dvinfo.net/conf/showthread.php?t=118782

http://www.dvinfo.net/conf/showthread.php?t=109425

Hi.

If you are referring to the gain on the camera, I've learned through these pages that they have to be fully open for line-in from the 302. Just to be clear, I'm referring to the mixer's gain controls. Are you saying that their needing to be near fully open is a known phenomenon as well?

John

My mistake, misread your post - I was referring to the camera gain, not the mixer.

I've just been experimenting, trying to make sure I'm not setting something up wrong.

Here's the situation. I've set up a Sennheiser EW100 G2 receiver line level input to my Sound Devices 302 mixer. I clip the lavaliere on my shirt and talk. To get a proper setting on the mixer, i.e. 0 to +6 (-20 to -12 on the camera) I have to fully open the gain. I've also set up the lavaliere transmitter and receiver at their most sensitive settings - receiver "AF OUT" at +12, transmitter "SENSIT" at 0.

I must be doing something wrong. (In case you're wondering, I'm using fresh batteries.)

Any thoughts?

Thanks.

John

Try using the tone generator in the mixer (0 or +4 dBu) to set the camera's level to FS then note the readings with the lav system connected to the mixer and compare to the level indication from the tone. If you have to go to max gain, so be it. Note that there are 2 opportunities to overdrive in a radio mic situation. The first is at the transmitter. Make sure that if you set the sensitivity to max the over deviation (audio peak) light never illuminates. If you meet that condition you have maximum allowable mic sensitivity and it remains to adjust the level into the mixer/camera using the controls on the receiver and mixer. If the transmitter is not over deviated you can safely set the receiver output level as high as it can go without worrying about overdriving the receiver but you can overdrive subsequent stages (mixer, camera). Their respective meters are there to prevent that.

John,
When you say fully open the gain on the mixer are you referring to the fader, the trim pot, or both? I use my Lectro 211s in line mode (+ 8) and with normal dialgue the trims end up at about 2 oclock and the fader is at 12 o'clock or more as needed. The 302 manual states that you want to set the trim pot so that the fader is aroiund 12 o'clock. The trim is thought of as a coarse adjustment to the gain structure, and the fader as a fine adjustment. If both have to be turned up all the way the only direction you can go when mixing is down. If you need more gain the only place to get it would be at the camera. The 302 inputs still go through the mic preamps in both mic and line so if the line level out of the receiver isn't high enough to give you a good gain structure experiment with the mic out settings and go mic in instead of line in. Hope this helps.
Benrie

Thanks for the replies and many suggestions. I’m afraid, though, that I still remain a bit confused.

Here again is my situation:

1) In the case of a boom mic, with the Sound Devices 302 set mic-in, I’m finding I have to set the gain near fully open (fader set at 0) to register between 0 and +6/8 on the meter (this to pick up a human voice at about two feet away).

2) When I use a Sennheiser EW 100 G2 lav, with the Sound Devices 302 set line-in, I face the same situation. In this case the transmitter and receiver were set at their most sensitive (transmitter SENSIT 0, receiver AF OUT +12).

3) If I set the mixer at mic-in and receive its signal from the receiver as mic level, I can get more latitude. To get between 0 and +6/8 on the meter I need only have the gain dial at about noon. (In this case I’ve changed the receiver AF OUT to –6.)

Perhaps these are just characteristics of the SD 302 but I doubt it. More than likely I’m doing something wrong but I sure can’t figure what.

Thanks again. I’m more in awe of the art of taking sound by the day.

John

p.s. In all these cases the camera has been set by the mixer’s tone and readings on mixer and camera seem to correspond properly.

i don't know wich lav are you using but i find that setting the sensitivity to 0 on the transmitter is way too high. you risk to clip the signal before it gets into the mixer. with senn mk 40, mk2, sanken cos 11 i usually set it to -20. i think i set the receiver's af out at -6 or 0 and set the input on the 302 to mic. plenty of space to play with the fader and gain pots. i should check though.. i'll let you know

pietro

I've inserted more thoughts into the body of the quote.
Regards,
Bernie

Hi John,
No, I don't think you have the gain staging right. I don't think your pots should be full up in the situations you describe. Since mic level seems to be working better with the G2, why not stick with that? Remember, the mic/line switch on the 302 is just an attentuator. For the short cable run you're talking about, you don't need to run line level.

As far as the Rode, I don't know. Maybe that mic just has a low output or something. I've never dealt with a condenser that needed that much gain though for normal dialog. Have you tried comparing the levels when using phantom from the mixer and the on-board battery in the mic to see if one is hotter than the other? It can make a significant difference with some mics.

hi john,
just checked. af out in my receiver is at -6, the 302 input is mic.

Something is not kosher here. In line mode this mixer has 35 dB gain when the controls are all the way CW. The 100 G2 puts out 12 dBu when its output is set to +12 before going into clipping when the transmitter is fully deviated. 12 + 35 = 47 dBu and that what you should get out of the mixer at a level just below what it takes to get the audio light to blink on the transmitter.

What happens when the receiver is connected directly to the camera? Do you read +12 on the camera at max output from the receiver? Is there some other way to check that the receiver is indeed putting out +12?

I do see something that makes me suspicious and that is that the mixer has transformer balanced input and the manual advises shorting one side of the input transformer (pin 3) for single ended input. The 100 G2 receivers are single ended and the 3.5 mm to XLR cable supplied with them does exactly this. Pin 2 is connected to tip and pins 1 and 3 to sleeve. What bothers me about this is that if you short one half the winding on a transformer the short is reflected to the other half and the secondary and the signal level drops dramatically. What bothers me about being bothered in this way is that the Sennheiser and Sound Devices manuals both recommend it. Does the circuitry sense that this has been done somehow and compensate for it? If I were doing single ended I would apply the signal across pins 2 and 3 and let pin 1 float. Note that this problem (real or immagined on my part) would not be a problem with active balanced circuits.

I've used the G2 with the SD302 (Countryman and Tram lavs) and as I recall, it did need a lot of gain, but not as much as John's reporting.

Hello.

Based on some suggestions and ideas you folks have offered, I’ve conducted a few experiments.

Experimenting with Sennheiser EW 100 G2

1) I attached the receiver directly to the Canon XH-A1 with the XLR set at line-in to see if the results would be different to those I was receiving on the mixer. I left the receiver set at AF OUT +12. When I spoke at normal voice with lav on my chest, etc. I had to open the camera level fully to get a -20 dB reading on the camera. This appears to be the same result I received when I attach the receiver line-in to the mixer.

2) I then changed the camera’s setting from line-in to mic and changed the receiver’s AF OUT from +12 to -6. With same voice etc. I can now get a full –12dB reading on the camera with the camera’s audio setting at only 3/9 open. This is similar to the result I get when changing the connection between mixer and receiver to mic-in.

From this experiment it would seem that the Sennheiser is performing the same way whether hooked up to 302 mixer or camera. My “solution”, I suppose, is to connect receiver to mixer mic-in.

Experimenting with Rode NTG 2 boom mic

1) Using a vacuum as a constant audio source (only thing I could think of in the house) I connected the Rode mic to mixer. To get a 0 VU reading on the mixer I had to set the gain fully open (fader left at 0).

2) Using the same vacuum noise I connected the Rode mic directly to the camera set at mic-in. Now I only had to open its audio level 4/9 to get –20 dB, the equivalent to 0 on the mixer.

Don’t see what “solution” I have here being that I have to connect boom mic to mixer.

(I also note that to set up the camera to receive line-in from the 302 the camera’s pots have to be fully open. That means I can’t use the camera levels to pump up the signal in example 1 above.)

I’m afraid another question seems to have emerged from these experiments. Over the past days on these pages I’ve learned, as I note above, that to set the Canon XH-A1 to receive line-in from the SD 302 the its pots have to be fully open. When I activate the 302’s tone I get -20dB on the camera’s meter. As 0 mixer equals -20 camera, I’m fully set. From then on I’m to look to keep the mixer readings from 0 to +6/8, which would be camera equivalents of -20 to -12.

With my vacuum experiment above what I noticed was that when the mic was reading 0 on the mixer I was getting a -12 reading on the camera not -20. Perhaps this just says something about the quality of the vacuum’s sound v.s. the tone generator. Makes me wonder though whether as I’ve been monitoring the mixer the camera hasn’t been reading hotter for other things too.

Ah!

Thanks.

John

The XLRM cable that comes with the G2 RX is for Mic level inputs.

The 302 has 60dB gain on the preamps, plus another 15dB gain on the fader.
Use the fader for more gain if you need it.

john

i would stick to this when using the mixer:
-input: mic, setting the receiver's af out at -6
-output: line, camera pots all the way open (as you said people experimented this and it is ok)
as for reading 0 at mixer's levels and -12 at camera's even after setting the tone at -20, this sound strange to me. are you reading vu only or vu and peak? i would check that although the vacuum is supposed to be a source of constant sound. during normal recording, like dialogs or interviews, the difference in reading vu only and peak is dramatic.
best

pietro

I might mention that an invaluable tool for doing this sort of testing is a "tone plug" or tone generator. I've got one of these ... http://www.trewaudio.com/store/produ...&cat=48&page=1, http://mixonline.com/mag/audio_gtc_industries_tone and it's far better than a turning on a vacuum (gotta give props for creativity with that one though) or humming when you need a constant level tone. Behringer's cable tester also has a sine wave tone generator built-in.

Would be interesting to plug one of these into the Canon's XLR mic input with the input level control set to "Auto" in order to discover the meter reading that the camera's designers felt represented the optimum recording level, then switch to manual mode and line level, replace the tone plug with the 302 sending 0VU tone on its meters, and see where you need to set the camera's input pots to produce the same meter reading.

Note that a VU meter and a peak meter read the same when they're fed a steady sine wave tone at the same average level. The differences come out when you feed a complex waveform such as speech and the degree to which they differ is dependent on the mix of frequencies and the dynamics of the waveform.

Could you try your tone plug on that and let us know what you find (unless you already know the answer)? A VU meter is to be calibrated to read 0 when connected across a 600 ohm load driven by a 0.7746 volt rms sin wave at 1 kHz. An average of 1 mW is delivered to the load under these conditions. But the peak voltage of such a sin wave is sqrt(2)*0.7746 = 1.09545V i.e. 3 dB higher than the rms voltage. If a peak meter really responds to the loudest sample it will read 3 dB higher. If it's "peak" measurement is really an average over a short period (a cycle or so) then it will read the same as the VU meter.

Yep, been there, done that and repeated the experiment as I write this. With my SD442 mixer, fed Tone Plug's 1kHz sine wave into input 1. Pan channel equally to L & R outputs. Fader to mid-point (0). Meter in VU mode. Adjusted coarse gain to produce steady state meter reading of 0VU. Toggled meter ballistics between all 4 options (VU, Peak, VU+Peak, Peak Hold) using front panel switch without touching any other settings. No change in meter indication in any of the 4 modes. However repeating the procedure replacing the tone source with a couple of regular microphones (A/T 3031 cardioid, Schoeps CMC641 hyper) and using my normal speaking voice, placing the meter in VU/Peak mode showed peak indications at about + 6dB when the VU section of the meter was hovering around 0dBVU

At first I thought that quite interesting then I realized that the next LED above 0 on the SD "meters" is +4 while the peak in a sin is only 3 dB above its rms (a sinewave is not very peaky at -1.5 on the peakiness scale - not dB). OTHOH voice is quite peaky (sample I looked at recently was at +12 on the peakiness scale). It just makes sense that the time period for a peak in the digital world would be 1 sample. No change would imply a window of at least half a millisecond (24 samples at 48K)

Thanks anyway!

On the 442 meters the LEDs represent 2dB steps from -14 up through +20 so the first LED above 0VU represents +2dB. But be that as it may, all I can do is report my observations. When carefully setting the channel gain and then the fader on a sine tone so they're set at the point when the 0 LED is illuminated and the +2 LED is just extinguished, there's no change in meter reading when switching the meter from VU to PPM ballistics - the +2LED remains dark. What else can I say? <grin>

My comment about 4 dB steps was drawn from the manual for the 302. Given 2 dB steps I go back to "quite interesting". For PPM the integration time constant is 5 ms so the observation is consistent. But for peak? There must also be a short time constant implied for that mode.