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BBC Stereo Requirement - Still MS?


chris_bollard

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Does anyone know if the BBC still requires stereo elements in deliverables to be recorded in MS?

I found this on their tech page which leads me to believe it still is:

"Stereo programmes must be recorded so as to be compatible for listeners in mono. In general signals should be in phase between channels. The S (difference) signal should rarely exceed the M (sum) signal (otherwise cancellation can result when the signal is heard in mono)."

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After a while of delivering M and S recordings and them never being used, I now deliver XY recordings. M and S recordings were just never included in any OMF/AAC exports, no matter how often I explained the decoding principle. With XY the director and editor can listen and gauge weather the recording works for them as it stands.  Communication is the key though, let your editor, director and post team know what to expect and if they sound good and work for the film they will use them. The directors and editors I've worked with for BBC projects aren't really sticklers for the rule book, and like pushing things.

Having said that… I've been referring to atmos recordings, if you're going to record a group of musicians or similar, i'd record it in MS and make sure they don't ditch the S track in the edit!

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Hi Chris, i've worked on various BBC radio programs in the past. This spec requires that your "program mix be mono compatible". What this means is that L and R should not have out of phase content that could completely cancel out when mixed down to mono. The reference to M and S comes from the tradition of PPM metering, where apart from using the PPM for level you can also set it to MS mode to check mono compatibility. Check out PPMulator as they have a very good software version of both PPM and MS settings. Ive attached a screen shot - If the yellow needle exceeds the white needle then there is out of phase content that will cancel out in mono. 

Best,

Ayush

PPM and MS.png

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Hi Chris, i've worked on various BBC radio programs in the past. This spec requires that your "program mix be mono compatible". What this means is that L and R should not have out of phase content that could completely cancel out when mixed down to mono. 

"Mono compatible" certainly includes not being 180 degrees out of phase, but I believe the primary reason for this spec is for mono compatible stereo considering both phase and levels, which would include M/S and X/Y, where the left and right signals have the same phase reference. The mono metering option helps keep the summed mono signal below maximum (summed left/right tracks will add up to 6dB), which is especially important with digital recording (virtually all recordings now) because an additional 6dB will easily cause an otherwise properly recorded stereo mix to clip when summed. Sonosax (and maybe some others) have incorporated summed mono metering for quite some time, though, sadly, too few understand the reason for this option and its benefit. Hopefully, the use of stereo in production tracks (even single person talking head) will return and grow in popularity, and manufacturers will start to include summed mono metering in their mixers and recorders.

Edited by Glen Trew
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