Re: mono->stereo effects, input gain handling and bypass
Re: mono->stereo effects, input gain handling and bypass
- Subject: Re: mono->stereo effects, input gain handling and bypass
- From: "James Chandler Jr" <email@hidden>
- Date: Wed, 9 Aug 2006 11:35:32 -0400
Interesting. AFAIK, a typical way analog mixers do stereo pan: When pan is
center, left and right are unity gain. When you pan right, turn down left
channel and vice-versa.
Maybe there are other better ways, since a stereo pan with this method would
alter perceived volume. But when panned center, am guessing one would want unity
gain on both stereo channels (to avoid mucking up the gain-staging), and I don't
think one would necessarily desire a channel boost over-unity when panned
off-center. Any over-unity gain could be bad on stereo sources that are already
peaking right up near the redline.
Maybe preserving perceived loudness is a 'lost cause' when panning stereo
sources, since radically different audio could be on left vs right. If left-hand
piano is panned down, it wouldn't improve perceived volume to boost the gain on
the right hand piano channel.
But often center-panned mono signals are attenuated -3 dB (to both channels),
and if hard-panned, one channel goes to zero and the other channel goes to unity
gain. That seems to agree with your findings. The mono scheme also avoids
over-unity gain, to avoid possible clipping on loud sources. If mono center-pan
involved +3 dB gain, it could be bad.
So maybe it is a quandary. The 'right thing to do' for mono-to-stereo would be
to duplicate the mono on both channels, which would give the boost on a mixer as
above-described. Its what would happen with an analog mixer if you use a Y cord
to connect a mono source to a stereo trackstrip. Dunno if a user would
appreciate his mono signal getting an automatic -3 dB attenuation when doing
mono-to-stereo, in the name of preserving perceived volume.
I allow mono or stereo FX in any FX chain in my hosting. If this isn't allowed
in a program, it is annoying if your only instance of a plugin is stereo and you
need to insert it to a mono track or vice-versa. The program MIGHT have a mono
plugin followed by a stereo plugin followed by another mono plugin. If
mono-to-stereo between-plugins duplicates the channel, and stereo-to-mono
attenuates the channels -6 dB then adds them, it doesn't lead to obvious gain
problems in a long FX chain with possible multiple conversions. If the signal is
a 1.0 peak sine, mono to stereo gives two 1.0 peak sines, then stereo to mono
gives 0.5 + 0.5 = 1.0.
In that case, doing something fancy to preserve perceived volume on conversions,
could compound gain-staging problems on a chain of plugins, depending on the
assortment of plugins that are chained? Maybe there is a much better way to
handle it though.
JCJR
----- Original Message -----
From: "James Closs" <email@hidden>
To: "tahome izwah" <email@hidden>
Cc: "CoreAudio API" <email@hidden>
Sent: Wednesday, August 09, 2006 10:30 AM
Subject: Re: mono->stereo effects, input gain handling and bypass
Hi,
I just do the following...
- set up a mono audio file generator in AU lab
- play an audio file through it (in this I have one peaking at -3db according
to the meters)
- now insert a mono->stereo apple matrix verb onto the track
- bypass the matrix verb
- my input signal is now peaking at 0db!
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