Dear Sir
I was interested to read in the AMPS Newsletter (No 9) that a working party has been set up to discuss signal levels when transferring digital sound rushes to analogue magnetic film. It seems to me that the first requirement is to have a standard flux level for 100% modulation agreed amongst the many sound transfer bays. During my career I spent some considerable time and effort attempting to do this, but to no avail.
However, as a past Chairman of the ISO Audio Committee on film sound I was able to bring together American and European sound level magnetic test films so that they were within 1 dB of each other for identical flux levels. The problems arises in the use of these films, with different transfer bays varying from 6 dB to 12 dB above reference level.
The American test films supplied by the SMPTE have a short circuit reference flux level of 185 nWb/m, and the signal output level on the film is 6 dB below reference. These films were developed for use in countries with a 60 Hz mains frequency and measured on a standard VU meter conforming to ANSI C16.5.
The European test films supplied by Agfa (and others) are measured differently and have a reference flux level of 320 nWb/m, and the signal output level on the film is 10 dB below reference. These films were developed for use in countries with a 50 Hz mains frequency and measured on a PPM conforming to EBU Tech 3205-E.
As I said earlier, the signal level section on both types of test film will replay within 1 dB of each other. If this information is already common knowledge amongst your Working Party, I apologise and can only claim that the sun on the Costa Del Sol has addled my brain. But the British Standards Institute would be most grateful if you would let them have details of any DAT-to-analogue transfer levels that you eventually decide upon.
John Aldred
Fuengirola
Spain