On 06/05/2013 10:57 PM, Fons Adriaensen 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
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):
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.
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