User manual

Page 42 User manual P1 Audio Processor
signal handling limit of +21dBu. There wouldn’t be much
point in protecting the digital recording chain if we could
accidentally clip the P1’s own circuitry.
The P1’s maximum output level is also set to achieve the
best distortion performance through the THAT VCA chip
which is at the very heart of the limiter. Lowest distortion is
achieved at or below +2dBu and is still very good at the
+7dBu limit we have set.
Q. You talk about levels in dB and in dBu. What’s the
difference? And what about dBFS?
A. dB’s are a relative measure of level, e.g. -6dB is 6dB lower
than 0dB.
dBu is an absolute measure of level within an analogue
system. 0dBu can be measured as a voltage and is always
0.775 volts RMS.
0dBFS is the maximum possible level of a digital audio
system.
Q. What is so useful about using dynamic threshold control in
the P1’s limiter design?
A. For a detailed answer, have a read of the P1 technical white
paper, but in summary;
In order to fully protect a digital recording system from digital
clipping, it is necessary to limit the maximum signal fed to the
recording system. However it sounds very unnatural to
instantaneously reduce the gain of a signal chain in order to
stop the overload occurring (this is what many traditional
limiters do). Sudden gain changes can introduce clicks into
the audio and also cause high levels of what’s called ripple
distortion.
The P1’s limiter uses three separate control side-chains
which vary the limiter threshold by up to 3dB below the