On Thu, Jun 06, 2013 at 01:32:08PM +0200, Jörn Nettingsmeier wrote:
gigaport hd+ connected to a micstasy line in at normal
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
So dynamic range should be 88.4 - 13 or around 75 dB.
No really impressive...
now if i feed it a white noise signal from JAAA at
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,
That would be a really invalid measurement. Peak / RMS ratio for
jaaa's noise generator is something like 12dB, so noise at -1 dB
RMS will be clipping as hell. That 12 dB is an implementation
limit, real gaussian noise has (in theory) an infinite peak / RMS
ratio. So better stay at -20 dB RMS or so.
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
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.
Very suspect. Should be interesting to record the waveform and
have a look at it (zita-scope would be handy, but not yet ready
for the real world).
a white noise steady-state spectrum shows a slight
raise of 2.5dB
around 6khz, and another hefty boost of 3.5dB around 14khz.
Again suspect, but see above. Could you try with a lower noise
General remark about the Jaaa screenshots: to measure noise you
should really use the noise, not peak, markers.
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)