6 Jun
2013
6 Jun
'13
1:32 p.m.
On 06/05/2013 10:57 PM, Fons Adriaensen wrote:
On Wed, Jun 05, 2013 at 04:25:56PM +0200, Jörn
Nettingsmeier wrote:
ok. now running on my laptop at 64x4 w/o xruns but at very low load.
for the measurements, i'm running off the battery to avoid hum issues,
but plugging it did not make any noticeable difference to me.
gigaport hd+ connected to a micstasy line in at normal Z (5.6kOhm
unbalanced) with a crappy rca to jack cable.
i chose 21.0dB amplification, because that should correspond to 0dBu at
full scale. indeed, it makes a -1.0dBFS sine wave from the gigaport come
out at roughly -14dBFS on the hdspm, which is what i'd expect going from
consumer (-10dBV) to pro equipment (+4dBu).
jnoisemeter reports -88.4 dB in flat mode with DC filter and slow
averaging response.
now if i feed it a white noise signal from JAAA at -1.0dBFS, the other
end reports a flat noise level of -13.1 dB, which as a rough guesstimate
gives us about 70dB of usable dynamic range. not great, but ok.
the -1.0dbFS sine tone at 1kHz shows a first harmonic at -95dB, and the
upper harmonics barely show in the noise, so we're fine here.
however, there is a thumping DC impulse every few seconds which clearly
shows up on the scope. it's clearly audible, not a show stopper, but
needs looking into. it's signal-dependent: when you don't generate a
sine-wave, it stops. complex signals either don't cause it or mask it
completely. might be a power issue. here's what it looks like (peak hold
and freeze, imagine this as a transient):
http://stackingdwarves.net/download/GigaportHD+%20Thumping%20noise%20over%2…
a white noise steady-state spectrum shows a slight raise of 2.5dB around
6khz, and another hefty boost of 3.5dB around 14khz.
so much for a quick run-through. if you want specific measurements or
have a pointer to proper measurement techniques, let me know.
best,
jörn
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio)
Tonmeister VDT
http://stackingdwarves.net
in case someone is looking for a similar problem
solver:
i just received an esi gigaport hd+, which is a usb1
class-compliant, bus powered audio interface that provides 8
discrete unbalanced audio outs. at 135€, it's not quite a steal, but
it solves one problem: to be able to listen to 5.1/7.1 content with
a laptop.
it works with jack out of the box and comes with two headphone outs,
one of which plays outs1/2, the other plays a pair-wise mix of all
eight outs. there is a row of flashing blue leds as "signal present"
indicators, although their threshold is a bit on the high side.
sound quality is appropriate, i gave it a quick listen and there is
nothing obviously wrong.
Interesting device... If and when you find the time, could you hook it
up to a Micstasy line input and Jaaa... ? 