Subject: Re: [linux-audio-dev] Writing a driver for this card: your thoughts?
From: Tim Orford (tim_AT_ipd50abcd9.speed.planet.nl)
Date: Tue May 28 2002 - 20:19:04 EEST
On Mon, May 27, 2002 at 10:48:28PM -0400, Lamar Owen wrote:
> Properly designed balanced in and out A/D and D/A converters can be completely
> immune to the PC's internal noise. But it all goes to proper design. The
> Antex SX series of cards likewise contain internal A/D converters. I have
> measured the noise figures of the Antex SX-36 we have at WGCR using state of
> the art audio systems analyzers, and the noise floor is below the LSB
> threshold. All due to balanced I/O, sound PC layout techniques, and top of
> the line components.
Just to try and put things in perspective, surely once you go beyond a certain
level, signal-unrelated noise is one of the least important indications of
sound quality? For me anyway. The quality of the noise is important
also :-)
> In a high RF environment, unless the converters are optically isolated from
> the PC, you might be asking for trouble. When I say 'high RF' I'm talking
> 10KW of AM transmitter fifteen feet away, with a measured RF field intensity
> of 105V/m (the ANSI exposure limit is around 645V/m). This means a one meter
> piece of wire that isn't properly grounded can develop 105V of RF energy. I
> have suffered RF burns of appreciable intensity touching wires that weren't
> connected to anything on either end -- they were just oriented along the
> field gradient.
your requirements do seem to be rather different than a recording studio
:-)
> Also, due to the processing typical radio stations use in the air chain, in
> many cases the quality of playback and record hardware for on-air use must be
> up to the top quality of a recording studio. Typical radio stations use
> sophisticated compressors, multiband limiters, and many other DSP-driven
> techniques to maximize loudness -- and when the dynamics of the source
> material go pianissimo, the compressors drive up the noise floor to
> compensate. Noise in the outputs of a broadcast automation or
> music-on-hard-drive system is verboten. [....]
such insane amounts of compression as used by most radio stations are not
usually related to 'quality' as understood by most poeple.
one of the most important aspects of analogue design is a good power
supply. Using a computer psu is going to severely limit what you are
going to achieve. Regulators are by no means perfect.
also, perhaps academic here, but using balanced
audio can actually degrade the sound by cancelling out even order
harmonics but leaving the odd order ones, or by increasing the component
count. Very high end stuff designed for non-hostile environments tends
to be unbalanced.
sorry if i'm just being pedantic :-)
cheers
Tim Orford
ok, back to trying to get Ardour compiled.....(does that make me
On-Topic now?)
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