[Ardour-Users] Ardour input level issues

Steven Chamberlain steven at pyro.eu.org
Wed Oct 24 10:39:54 PDT 2007

John Rigg wrote:
> Are you sure about this?

No. :D
But I thought the reason for Thomas' meters appearing to show different
readings, could have been something similar to what I was experiencing.

It has now occurred to me that Ardour uses peak meter whereas the
Behringer mixer is probably a digital VU meter?  I would therefore try
putting a 1000Hz sine wave into the mixer, set it to '0dB' on the mixer,
then check what Ardour displays.

> Ardour measures levels relative to digital full scale (dB FS),
> which on a Delta 1010 is around +20dBu.

> What people forget is that dB is just a ratio. Without stating what
> the reference is, it's meaningless.

I thought I understood that, but perhaps not.

> Don't confuse 0dB FS with 0 dBu - they're completely different (20dB
> different in this case).

I think that's the part I may have misunderstood.

Isn't 0dBFS 'supposed' to be the same as 0dBu in a 'normal' setup (hence
the reason for having standard line levels of +4dBV and -10dBV)?

I assumed that the Delta 1010 trying to 'cheat' in some way, sacrificing
accuracy of its ADCs for very quiet signals, in order to avoid
distortion when a sound source is allowed to exceed 0dBu.

> 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.

Yes, I believe it would throw away 20dB of dynamic range on the inputs
and outputs.  I was *hoping* it wouldn't be important considering the
SNR of either my desk or sound card, but I'm open to suggestion here.

Is it true that 24 bits theoretically encode 144dB, and less the 20dB
which I am not using this would be 124dB of dynamic range?  I'm not able
to measure the SNR of my setup right now but I would probably assume
between 100-120dB.  Or should I expect to achieve a better (higher) SNR
by using that extra 20dB above 0dBu.  I'd imagine it depends on the
source of the noise, which won't be the same in all situations.

My intention was to have the meters in all of my audio software match up
with the meters on my desk.  I simply found it annoying to have the
meters on my desk not match the meters in Ardour and other audio
software.  Is that sensible?

Steven Chamberlain
steven at pyro.eu.org

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