[LAU] interfaces with electronic gain controls

Len Ovens len at ovenwerks.net
Thu Aug 2 20:54:43 CEST 2018

On Thu, 2 Aug 2018, Chris Caudle wrote:

> Out of all the interfaces mentioned recently as working well under linux,
> all I have looked up seem to still use potentiometers to set gain.  That
> is fine for recording mono instruments or vocals, but for stereo or
> surround acoustic recording I would really like an interface which allows
> for very close gain matching between channels, or at the very least very
> repeatable gain settings so that I can correct in post production if
> needed.

Two things:
look for a switch that controls two channels from one pot. This might be 
called dual, link or stereo. I do not know how close this puts the two 
channels but even my cheap Art USBDualTubePre has that.

If the device doesn't even have that... set both channels full up as that 
is the one place they _should_ match. A matched pad to lower levels could 
be added if needed.

However, (the bad part) I suspect anything under about $1k (or higher for 
larger channel counts) will have gains that track poorly in any case 
because the componants from channel to channel are not matched.

You could try the rack version of the x32 mixer series (XR18), (or the 
soundcraft and A&H versions) basically anything that is also meant to be a 
live mixer. Some of them will already have stereo channels (at line level) 
that should be matched. I should note that the XR12 and XR16 have only 2 
channels on the USB, the XR18 has 18 and the x32 rack has 32. They all 
seem to have network based control. If they don't have browser control, I 
was able to find the OSC map for these devices in their DL files.

The price is still high and you are paying for a lot of lower quality 
channels rather than fewer high quality channels.

I am not sure if your choice of USB is for laptop use or "thats what I can 
find" reasons. If you can use a PCIe device, I was going to suggest a 4 
channel (two stereo stream) audioscience card, but the ASI5620 is already 
$1k. Audio Science has had Linux drivers forever. Diggram and Lynx not so 
much but some of the cards are less pricy too. I know that there are now 
some Digigram modules for Linux but you would have to check for each card 
you are interested in.

You are right, though, there is not much out there. I suspect that digital 
mixers are the best bet for you though. most of the smaller 4 channel USB 
boxes use phyical pots for easy macos (USB2.0) compatability.

Len Ovens

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