Re: What Mid-range USB Sound Cards Work with Linux?

[rlharris@oplink.net]

On Sat, May 28, 2016 1:17 pm, Martin McCormick wrote:
> I am not using XLR's, but I do use 1-to-1 isolation transformers
> between the audio sources and sound inputs

Hum in audio systems almost always is a consequence of improper grounding.
 Although an XLR connector on a piece of apparatus SHOULD BE a guarantee
of freedom from hum, such is not always the case; regrettably, not every
audio manufacturer has a proper understanding of grounding and shielding,
and of the distinction between a signal ground and a chassis ground.

Perhaps the best comprehensive collection of application notes is that
made available by Rane, at http://www.rane.com/library.html; the notes
are:

RaneNote "Grounding and Shielding Audio Devices"
(updated 7-02)

RaneNote "Sound System Interconnection"
(RaneNote 110) (updated 7-11)

RaneNote "Why Not Wye?" (updated 4-04)

RaneNote "Pin 1 Revisited" (8-07)

RaneNote "SCIN: Shield Current Induced Noise" (8-07)

PDF "Grounding and Shielding Computer-Controlled Audio Devices"
Steven Macatee, AES (12-94)

PDF "System Problems and Equipment Manufacturers"
Bill Whitlock, Systems Contractor News (9-87)

PDF Cable Outlook: Is it time to move to shielded category cable?
SVC 7-13 (400k)

Various manufacturers offer isolation transformers and level converters to
enable interconnection of consumer (-10 dBV RCA) and professional (+4 dBu
XLR) devices.  For example, Rane has the passive "Balance Buddy", and ART
has the "CleanBox", which utilizes active circuitry.  Such devices are
inexpensive, and can be had from most commercial broadcast supply houses.

RLH