[grc] What sound card worked best with Rivendell for you?

[al davis]

On Fri, 15 Sep 2017 22:59:44 -0300
Max via grc <grc at maillist.peak.org> wrote:
> So what's y'all's experience WITH PCI-E sound cards for Rivendell?

My favorite PCI-E sound card is the Asus Xonar DX.  It's about $90, so
it is not the cheapest.  I am tempted to try some of the cheaper Asus
cards to see how they compare.

This one has 4 outputs, 7.1 full surround, which Rivendell can use as 4
separate outputs, which I do.  My preference is to use the "front" for
cue, and others for main rdairplay, one for scheduled playout with
rdcatch, one for a secondary output from rdairplay.

It's a 12 volt card, using a separate power cable, so it has more
output, and more input headroom than the cheaper 5 volt cards.  Asus
makes big claims about how much cleaner it is than the onboard audio.
It does sound good, but it is still unbalanced "consumer" levels.  At
least it's "good consumer" (12 volt), which is better than "cheap
consumer" (5 volt).

> Does it have to be better than a 5.1 channel in your experience?

I get a 7.1 card.  A simple card, with just a single output, will work,
but Rivendell supports multiple outputs if the card has them.

I usually use 4 faders on the console for the computer.  One is for the
traditional computer things like Audacity.  One is the main rdairplay
output.  One is for "cue" and "rdlibrary".  I use a fader for this,
which you can put in cue or even on air when you need it.  The other is
for the playback decks in rdcatch, which can be synced with record
decks and can put things like live stuff on the air.

> If so, what cards gave the best dynamic range and surge resistance and
> impedance mismatch tolerance and good drivers support in Linux especially
> Debian ?

Most cards worn under ALSA, but some seem to have quirks, and some
don't split out the surround as I would like.  The digital in and out
might be like separate cards, maybe used separately.  You need to
experiment.

I wrote up a technical explanation for some of this here:
http://communityradio.wiki/dokuwiki/doku.php?id=radio:soundcard

Dynamic range .. look for the extra plug, more voltage, more power,
more dynamic range.  

"impedance mismatch tolerance??"  This really isn't a problem.
Headroom and levels are the real issue.  

You can get a higher output level if you need it by adding an external
amp, but it really shouldn't be needed in most cases.  One case
where you might need it is with a so-called pro console designed for +4
inputs that doesn't have gain trims.  A more important case where you
might need it is to drive the transmitter, which is always designed for
the traditional pro +4 average, +24 (or better) peak levels.  If you
don't have that kind of level the processor probably won't work as well.
You might need "balanced" for a long cable.  Even most "balanced" sound
cards don't do the real pro levels.  Some are as low as +4 peak, which
is really the cheap 5 volt stuff with an inverter, and they call it
balanced.

My company http://kaatskit.com makes a quad line amp that can be used
for this, or as a distribution amp, or related stuff.  It's $75 kit,
$150 assembled, 1/3 off if purchased with a console.

The other concern is the input.  All of the consumer cards have
unbalanced inputs designed for relatively low consumer levels.
Anything with pro output levels will probably overdrive the input
stage, ahead of the volume control.  You need to cut it down
externally, and figure out how to deal with the unbalanced input from a
so-called balanced source.

There are at least 3 variants of the balanced outputs from consoles and
the like, requiring 3 different ways to deal with how to drive
something unbalanced.

It could be "floating", like a transformer.  Just ground one side.
It's easy.  This configuration has another advantage in that it breaks
ground loops, which are often a problem with unbalanced audio.  Some
consoles (Kaatskit, some but not all Audioarts) have "active floating"
outputs, which mostly you can treat like a transformer.  That's
"mostly".  It doesn't deal with extreme cases like 200 mile phone lines
or cases where there is 100 volts between one ground and the other.
For that, only a real transformer works.

It could be "non-floating", driving both sides hard, forcing balance.
In this case, to feed an unbalanced load, you take one side to ground.
So your feed is now just plain unbalanced, and prone to ground
problems.  If you ground one side you could damage it.

It could be "impedance balanced", which forces impedance balance, but
drives only one side.  It works great feeding a balanced input. Feeding
an unbalanced input it works just like unbalanced.  This is common on
the "band" mixers.  (Behringer, Mackie, Soundcraft, etc.)

The one you need to watch, the least flexible, is the non-floating
balanced that is used on a lot of pro equipment.  You may need to add
an amp in line to get the noise down.


Anyway .. back to the original question ..  I like the Asus Xonar DX.
Asus motherboards with the 6 audio jacks work good too, but at the
lower "5 volt" levels.

On calibration, setting the levels on the sound card ....   Usually
what works best is to set everything to "0 db".  Sometimes (usually
for playback) this is all the way up.  Sometimes (usually for
"capture") all the way down.  Sometimes it's in the middle. This is
deluxe.