Re: [LAU] turning a consumer soundcard into "prosumer" w/ quasi-balanced outs

From: <fons@email-addr-hidden>
Date: Wed Jun 09 2010 - 22:37:41 EEST

On Wed, Jun 09, 2010 at 11:45:10AM -0700, Niels Mayer wrote:

> FYI, I just got and installed the Terratec DMX6Fire -- definitely a
> better alternative for Linux as you can use "envy24control" to control
> the card, instead of the confusing and error-inducing alsamixer. Plus
> you get an extra MIDI I/O, spdif and toslink I/O, etc. Overall, an
> excellent $20.00 card, perhaps even preferable to the equivalent
> M-Audio Delta 66.
>
> The card's performance seems in line with it's specs (
> http://www.soundonsound.com/sos/Apr02/articles/terratecdmx6.asp )
> "A-D converters: 24-bit 64x oversampling (part of AK4524 chip).
> Input dynamic range: 100dB (converters only)."
>
> With the waveblaster connected to the db50xg, but no output coming
> from the synth-card, here's what the noise looks like:
> http://nielsmayer.com/npm/jaaa-DMX6Fire-L-fullband-db50xg.png
> http://nielsmayer.com/npm/jaaa-DMX6Fire-L-lowfreq-db50xg.png
> http://nielsmayer.com/npm/jaaa-DMX6Fire-R-fullband-db50xg.png
> http://nielsmayer.com/npm/jaaa-DMX6Fire-R-lowfreq-db50xg.png

Looks decent. If some of the small peaks in the LF plots are
mains related, you grid frequency seems to be 115 Hz...

> (above tests set with input amplification for the A/D set at 126/163
> in envy24control, which seems to handle the full-output of the loudest
> of my XG-midi test files without clipping... you can make the noise
> disappear entirely (or at least go below -160db) by turning the A/D
> amplification below 60/163.)

'Canonical' settings for this chip are 0x7F (127) for input and
output. The range 128-163 is used by some cards to control additional
input gain.

> Subjectively, however, the sound is not better! Although cleaner and
> more noise free (the other dx-sc51 would light up the lowest level
> -60db output metering LED's on my external DAC ... this one doesn't)
> this card doesn't actually sound as "punchy" as the same synth playing
> through the crap Dynex dx-sc51. Especially interesting is that the
> card sounded particularly anemic&shrill when I first plugged it in,
> but as it ran overnight it now sounds much better (electrolytic
> capacitors might have been in storage for a while on this used card).
> (For all my listening tests, I'm using TOSLINK outputs into a higher
> quality external D/A, so the only change is the sound of the A/D and
> analog inputs, not the D/A or outputs).
>
> By lacking "punch" i mean that the bass-transients sound somewhat
> "round" and "soft" . Bass drum doesn't have a forceful "kick" to it.
> And likewise a there's little "snap" to the attack portion of the
> bass. On the other hand, the high-end sounds a little brighter and
> less "veiled" but sometimes shrill. To improve the bass-response, I'm
> considering changing some of the input decoupling electrolytics to
> larger values. The JRC4580 op-amps are surface mounted and therefore
> difficult to replace. (Nonetheless, people have replaced the opamps
> and caps on this board and claim/measure an improvement:
> http://forum.rightmark.org/topic.cgi?id=4:122 )

Changing the caps (if they are indeed that old) could help.

> Perhaps the input op-amps on the Dmx6fire are "slew limiting"

Could be, but that would be quite bad design. In particular if
that card can do 96 kHz as well, as I assume it does.

I can't really comment on 'subjective' descriptions. Since you
are quite emotionally involved, and this is not a blind test,
chances are 99.99% that 'it's all in your head'. Or you prefer
lower quality sound :-)

If an electronic circuit does things like 'removing (or adding)
punch', that must be explained. There is a limit to what simple
circuits can do, and whatever they do can and should be measured.

If subjective claims turn out to be reliable (and this can be
verified only by blind tests), there will be something that
can be confirmed by measurement.

Ciao,

-- 
FA
O tu, che porte, correndo si ?
E guerra e morte !
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Received on Thu Jun 10 00:15:02 2010

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