Recording Parallel on two channels with one lower, for safety

paulears

paulears

Veteran
I note in many topics people mentioning this way of working. I'm curious as to how common it is, and why? Usually I have two mics, or a stereo mic on the go, but when I do feed one mic to both channels of a camera, I usually set a manual level on one, and leave the other on auto, or even switch in the limiter for safety. Over the years the 'problem' got better, with me able to keep an eye on the manual levels in the v/f.


Why is the -10dB system, often mentioned becoming more common? Is it a DSLR thing, where the sound facilities seem very poor, or just a new technique? Doing it this way had never occurred to me. I tried it out, but discovered I still needed to adjust the levels with both on manual and in post instead of the constant loud auto/limited audio track on ch 2, I got two channels that needed more work.

Anyone using the technique care to share the advantages?
 
I've only used it for specific situations, where the levels could be very dynamic, or I didn't have access to a good limiter. The reason I can see for doing it more frequently would be if you can't monitor or adjust the levels while you're recording, such as might be the case for people doing everything themselves - filming with a cam mic. Otherwise, it would create more work in post, and possibly lead to less care when adjusting levels.
 
The technique was used many years ago in tape based recording formats (BVU, Betacam etc) where track 1 was at the edge of the tape and track 2 was in a bit, if there was tape damage the other track could be used, also in those days s/n of some tape formats were quite poor so you tried to push the levels to get the best s/n and often hit clipping point. With track 2 at a lower level often this would save the day.
I still use the technique in the digital world but do it a bit differently than just setting the level lower on the camera, I set BOTH inputs into the camera / recorder at the 'correct level' and equal.
With one mic for example I will pan it a little to the 'left' which actually reduces the 'right' channel level by whatever is needed..... This then allows 2 mics (when needed) to then be to be panned 1 to left and 2 to right without further adjusting the levels on the camera.

I use a SD442 mixer and occasionally a FP33 mixer, this techniques works well with most stereo mixers with pan controls (not switches).
 
I've tried this technique a few times, but I've never found it useful for what I shoot. Setting my normal recording level to peak at -12 dB, I've never had anything clip on any of my shoots over the past 5 years. Part of this is probably due to the excellent 2-stage limiter built into the Sound Devices MixPre mixer, and recently part of this might be the surprizingly good limiter built into the Panasonic GH3 camera. ( when I skip the MixPre-D mixer and go direct from Sennheiser UHF lav packs ) Maybe I'm just lucky... :-)
 
Dual mono recording (sending the same signal to two separate channels to be recorded at two different levels) is used as a safety for the low budget one-man/woman sound crew since s/he can't boom and mix at the same time, and they are using consumer or prosumer gear that most likely has a mediocre limiter at best - not to mention the fact that they are probably working with an inexperienced director, cast and crew - so every take is really important, as there will most probably not be a professional doing the audio post.
 
I see this as a multi-part answer. When I got back into video, I realized that until I got better with sound, and also being a one-man band, having another track with a little more head room made sense. I picked up on this with a cheap TASCAM DR40 that actually has the feature built in. You can set the unit up for manual, with the one track lower than the primary. I actually find this comforting when I am recording an interview and I want to make sure I have a great back-up, I also run lavalier's to the TASCAM as well as the HPX-250 via XLR cable. It especially comes in handy if you are doing a live speech and you have one shot for memorable comments. I would be reluctant to ever use the complete auto circuitry in any DSLR or consumer camera.
 
It's a revived technique on the forums, for many stills photogs and new ppl just getting into audio for the first time.

For them, if you're just recording an interview, with little experience, during a test, you can set a 'correct level' from the 2 ppl so you don't have to alter the record levels during the take. But keep an eye it.

However any recordings, say film dialogues where there will be some altercation, it's limiters all around. But even then you need some experience setting levels before the start.

Without limiters, setting TK 2 at 10dB down is the next best thing. The increased 'loud level' is never the same each time, and you might need to make it 14dB for safety, but 10dB is the nominal figure, for safety.

The trick is to remember your best recordings, what gear and how and what you did. Gradually that totals up to become your experience for each new job.

Cheers.
 
Personally I've never done this but there again I have always been very careful with levels and set them with enough headroom and with the advantage of experience.

I can see it being useful for the DSLR shooters or people who do not have a lot of experience of how loud things can go and it was certainly more useful in the analogue domain where headroom was possibly less.

I have panasonic P2 cameras and like others they use digital level scaling so if I tend to follow broadcast levels with line up at -18dbfs and peak to around -10dbfs there is still 8db's of headroom available before max level.

What I do also use is the limiters in my camera as they are excellent and even the auto gain can be a godsend at times and never seems to overload.

I also have the advantage of several quality mixers with very good limiters so can record split track on the camera if I need to with direct radio mic and cam mic (for ambience) to two channels and a mic to channels 3+4.

People also have to remember that in digital scaling and recording you do not need to peak to 0dbfs as there is plenty of dynamic range and if anything under modding digital can make it quieter.

Here is a clip of a footie match I did recently and I forgot to turn off the auto gain on the cam mic channel but it does a pretty good job of the mega levels of the crowd and there is little evidence of distortion:
http://www.youtube.com/watch?v=ibGx1YdBW6o
 
I can confirm that unclebob is dead on the money. That and you've got two inputs available from one audio source, so what you gunna do, just leave da udda one empty?
 
As a sound newb with an FS100 and mainly a single shotgun I do this all the time - in fact love that you can

Mainly ive got a reporter or a stand booming so my options for ramping sound levels during a take are minimal without disturbing my operation of the camera

Gives protection if the subject gets very animated or starts laughing etc that might clip the 'main' channel - the second is down a bit..

S
 
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