Re: Understanding PPM Meters

In the perfect world any peak at or below max would be proper which is,
indeed, the case when going directly to most modern recorders. However,
due to limitations in certain chains of events - particularly for
broadcast when a satelite uplink is used, less dynamic range is usually
required and requested.

However, if you limit the peaks as displayed on a peak meter to the 0VU
reference, your average level will probably be too low. For broadcast
uplinks it seems that, after sending a 0VU reference alignment tone,
riding gain to keep peaks below 10dB over 0VU reference makes everyone
happy.

The standard of -8dB for 0VU reference with +4 being the max goes back
to the standard used by the old analog Nagra machines (and others) of
allowing peaks of 12dB over 0VU (this has also carried over as a final
product standard for music, which is why the -12dB curser was still an
option on DAT machines - but should not be used for recording original
tracks). Part of the reason for this standard was to overcome the
effects of tape noise, which is no longer in the equation.

However, the Cooper CS-104 and Filmtech LSP4 mixers allow up to 20dB
over their -8dB 0VU reference (using peak meters) before clipping
occurs. For this reason, I generally like to the align the indicated
-8dB on the mixers to -20dBfs on digital recorders, getting the most
out of the mixer and recorder.

Glen Trew

.

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