On Thu, Jun 06, 2013 at 01:32:08PM +0200, Jörn Nettingsmeier wrote: > 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. 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 -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. 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. OK. > 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. 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 level ? General remark about the Jaaa screenshots: to measure noise you should really use the noise, not peak, markers. Ciao, -- FA 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) _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
