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How are analog and digital signal levels aligned to loudspeaker acoustical output?

In Europe, 0 dBu is aligned to -18 dBFS (ITU/EBU standard). In the US and Japan, +4 dBu is aligned to -20 dBFS (SMPTE standard). So the European alignment has a 9 dB lower analog signal level for the same digital scale level. This results in a higher analog headroom but at a cost of a higher noise floor. These alignments are not a function of the loudspeaker but of the source - see picture below.

Analog, digital and acoustical scaling

Next the signal is aligned to an acoustical output of the loudspeaker that results in the required level at the listening position. Here is the complete process:

 A 0 dBu pink noise alignment signal is input to the mixing console
 The gain is then trimmed somewhere in the desk so that the metering displays -18 dBFS or -20 dBFS
 Then each loudspeaker’s input sensitivity is trimmed so that the reproduced acoustical level at the listening position with this signal is:
 85 dB SPL (used for the movie industry) or,
 79-83 dB SPL (used for the broadcast industry due to the lower replay levels at home).
This measurement is conducted using a sound level meter set to “C-weighted” and “Slow”.

All the loudspeakers have an input attenuator (after the D-A converter in digital input versions) that allows the acoustical output to be adjusted so that it can achieve these reference levels in typical conditions with these input signals.



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