[Ardour-Users] Ardour input level issues

[John Rigg]

On Wed, Oct 24, 2007 at 01:11:20PM +0100, Steven Chamberlain wrote:
> One other thing to look out for, is that some cards (such as my Delta
> 1010) try to add extra headroom.  My Delta 1010 reports its input
> signals as being 20dB lower than they really are; likewise, when playing
> back it plays them 20dB louder than Ardour expects.  The idea was
> probably to avoid clipping if the input signal goes slightly above 0dB.
>  I add +20dB Simple Amplifier plugins to each of my 'input' tracks in
> Ardour, and a -20dB Simple Amplifier plugin to my outputs, to compensate
> for this.

Are you sure about this? Ardour measures levels relative to digital
full scale (dB FS), which on a Delta 1010 is around +20dBu. dBu is
relative to 0.775mV rms, which dates back to the days when analogue
gear had 600 ohm input impedances (0.775mv equates to 1mW into 600 ohms).
Don't confuse 0dB FS with 0 dBu - they're completely different (20dB
different in this case).

What people forget is that dB is just a ratio. Without stating what
the reference is, it's meaningless. Steven, I suspect that by adding
those amplifier plugins you're wasting the top 20dB of resolution
in your Delta 1010s, and effectively using only the lower 20 bits
or so.

John