Ganged controls
Operationally, when you use two channels ganged together on one fader to control the overall level of the stereo signal, you must also ensure that the limiters on both the channels are ganged. Should this facet of the operation be overlooked then, if one channel is louder than the other and peaks to a level where it ‘hits’ the limiter whilst the other does not, there will be a shift of sound image.
Additional mixer stereo facilities
All incoming sources must be in phase, and to overcome any problems you should always carry at least one phase reverse cable, although the mixer will almost certainly provide a switchable phase reverse on at least one channel. Other facilities available with the mixer should include the ability to change A/B inputs to M/S, and vice versa, with appropriate monitoring. There may also be controls on the mixer to vary the ‘width’ of the mic input. Stereo mics tend to take more power than mono, so batteries won't last as long using phantom power via the mixer; do make sure you carry sufficient spares.
Cabling and identification
When cabling to the camcorder, most recordists adopt the convention of colour coding: red for left (track 1) and green for right (track 2). It is essential to double check all your connections to avoid any possibility of confusion at a later stage. More importantly, note on both cassette box and label whether you've recorded M/S or A/B. Verbally identify the beginning of each cassette (after bars and tone) with the same information, or add this information to the clapper board if one is in use, just to be on the safe side.
Levels
Another area where there is a variance of opinion amongst professionals is the preferred recording level, complicated by the need to provide a mono-compatible signal (a good reason to use M/S on location). A full consideration of this subject is beyond the scope of this handbook, but to minimize the possibility of hitting limiters (not ganged!) in the camcorder chain, it's probably safest to under-record by at least 3 dB. Therefore, line-up tone should be no higher than –20 dB on the bar meter, and preferably below, some recordists opting for as low as –24 dB. Stereo tone will ident at least one channel, the simplest ident being a cut in the left channel, and should always be used to indicate a stereo signal.
The mixer should have good quality meters (often two PPMs) but these take experience to read and interpret for stereo signals. It is not always easy to determine that you are providing the desired output, since they give no hint of phase errors for example. Remember, if you're monitoring M/S, the S signal will be much lower than the M signal. Listening to stereo on headphones on location also takes experience to recognize the desired levels and any discrepancies that arise due to phase errors.
More often than not, the quality of meters on camcorders leaves something to be desired, another reason for erring on the side of under-recording your levels. Since the spectre of unreliability rears its ugly head, especially where onboard limiters are concerned, for any stereo production you should insist on recording on a separate broadcast quality recorder, such as DAT. Or you can use a mixer with an onboard hard disc recorder. In both instances you can revert to recording a reasonable signal level, and leave the camcorder tracks solely as a back-up and editing guide.
Mono compatibility
If you are recording in stereo (as opposed to mono dialogue to be placed in an ambient sound stage), you must separately monitor all sections that require mono compatibility. When you hear individual performers within a stereo image, their position within that image assists in defining their contribution, but in mono, their rendition may simply ‘blur’ into the whole of the aural surround. The visual equivalent is the difference between colour and black and white framing. In colour a person wearing red clothing will easily stand out from a blue background, but in black and white the two colours may simply merge together in similar shades of grey. So, for mono compatibility, as with black and white, you must monitor the whole in that medium.