-6db limit when recording mono signal to computer... what gives?

[Jake Fallon]

I own an M-Audio Firewire 1814 interface and am pleased with it,
however, If i try to record a mono signal (48 kHz - 16 bit), i notice
that the maximum signal that I can record is only -6db. Even with the
mic pre turned all the way up, i the computer acts as if there is some
sort of limiter in the signal path even though there definatly is not.
(I have my Rhodes NT-2 mic plugged directly into the M-Audio Firewire
1814's front XLR input. The 1814 is then plugged directly into my
computer via firewire.) Now, when I monitor my recording levels (using
Adobe Audition), i notice that even with the mic pre turned all the
way up (yes, the preamp is clipping now), the computer somehow is
limiting the signal to -6db when it should be peaking out on the
computer.

What in the world is causing this?

A workaround that I've figured out is to record a STEREO signal (48
kHz - 16 bit) and now I get full headroom, but why can't I simply
record a mono signal and have it work properly? Also, I've noticed
this on my home studio and on our studio at the office. Both machines
are running XP pro and are plenty fast.

Any advice would be GREATLY appreciated! Please either respond to this
post or email me at: (remove
-NOSPAM-) THANKS!

-Jake

[Paul Stamler]

"Jake Fallon" > wrote in message
om...
> I own an M-Audio Firewire 1814 interface and am pleased with it,
> however, If i try to record a mono signal (48 kHz - 16 bit), i notice
> that the maximum signal that I can record is only -6db. Even with the
> mic pre turned all the way up, i the computer acts as if there is some
> sort of limiter in the signal path even though there definatly is not.
> (I have my Rhodes NT-2 mic plugged directly into the M-Audio Firewire
> 1814's front XLR input. The 1814 is then plugged directly into my
> computer via firewire.) Now, when I monitor my recording levels (using
> Adobe Audition), i notice that even with the mic pre turned all the
> way up (yes, the preamp is clipping now), the computer somehow is
> limiting the signal to -6db when it should be peaking out on the
> computer.
>
> What in the world is causing this?
>
> A workaround that I've figured out is to record a STEREO signal (48
> kHz - 16 bit) and now I get full headroom, but why can't I simply
> record a mono signal and have it work properly? Also, I've noticed
> this on my home studio and on our studio at the office. Both machines
> are running XP pro and are plenty fast.

What's going on is that when you record in mono, the software assumes that
you have signal coming in both channels and want to sum those down to a mono
signal. If you did that with two full-scale signals, the sum would be up to
6dB too hot and clip like crazy, so it automatically pads each signal down
6dB. Of course, since you don't really have something coming in the second
channel, you're just getting the first channel's signal 6dB down (plus a
tiny bit of noise from the inactive second channel).

You've found the proper work-around, or at least the one I use. The second
step is not to save the stereo file, but rather to highlight the channel
that actually has signal in it and export that to a file. (Alt-F-E, I
believe.) Now you have a nice mono file with only one extra step involved,
which'll take all of 2 seconds. Be sure, after you do this, to click
someplace in the center of the screen so that both channels are active
again; otherwise the next take will be recorded only to the channel you
previously highlighted -- 6dB down.

PITA, yes, but that's how CoolEdit/Audition works. Many of the Windows
editing programs I've seen work the same way.

Peace,
Paul

[Paul Stamler]

"Jake Fallon" > wrote in message
om...
> I own an M-Audio Firewire 1814 interface and am pleased with it,
> however, If i try to record a mono signal (48 kHz - 16 bit), i notice
> that the maximum signal that I can record is only -6db. Even with the
> mic pre turned all the way up, i the computer acts as if there is some
> sort of limiter in the signal path even though there definatly is not.
> (I have my Rhodes NT-2 mic plugged directly into the M-Audio Firewire
> 1814's front XLR input. The 1814 is then plugged directly into my
> computer via firewire.) Now, when I monitor my recording levels (using
> Adobe Audition), i notice that even with the mic pre turned all the
> way up (yes, the preamp is clipping now), the computer somehow is
> limiting the signal to -6db when it should be peaking out on the
> computer.
>
> What in the world is causing this?
>
> A workaround that I've figured out is to record a STEREO signal (48
> kHz - 16 bit) and now I get full headroom, but why can't I simply
> record a mono signal and have it work properly? Also, I've noticed
> this on my home studio and on our studio at the office. Both machines
> are running XP pro and are plenty fast.

What's going on is that when you record in mono, the software assumes that
you have signal coming in both channels and want to sum those down to a mono
signal. If you did that with two full-scale signals, the sum would be up to
6dB too hot and clip like crazy, so it automatically pads each signal down
6dB. Of course, since you don't really have something coming in the second
channel, you're just getting the first channel's signal 6dB down (plus a
tiny bit of noise from the inactive second channel).

You've found the proper work-around, or at least the one I use. The second
step is not to save the stereo file, but rather to highlight the channel
that actually has signal in it and export that to a file. (Alt-F-E, I
believe.) Now you have a nice mono file with only one extra step involved,
which'll take all of 2 seconds. Be sure, after you do this, to click
someplace in the center of the screen so that both channels are active
again; otherwise the next take will be recorded only to the channel you
previously highlighted -- 6dB down.

PITA, yes, but that's how CoolEdit/Audition works. Many of the Windows
editing programs I've seen work the same way.

Peace,
Paul