Search found 22 matches

by nettings
Sun Sep 24, 2017 2:49 am
Forum: Octo Sound Card for the Pi
Topic: Some measurements...
Replies: 8
Views: 6084

Re: Some measurements...

Total harmonic distortion of an 1kHz sinewave at -3.8 dBFS: Distortion spectrum.png A rough sum of the harmonics yields a THD value of 0.00018. Not impressive, but certainly not enough to be worrisome given that the signal will eventually hit a speaker :) Mostly odd harmonics, though, so don't expec...
by nettings
Sun Sep 24, 2017 2:29 am
Forum: Octo Sound Card for the Pi
Topic: Some measurements...
Replies: 8
Views: 6084

Re: Some measurements...

For comparison, here is the HifiBerry DAC+ Pro XLR, measured through a different preamp (Direct Out Andiamo), but with comparable gain structure: HifiBerry-DAC+ left channel, silence + zita-resampler.png Still a different league, but if the Octo could lose its weird bumps below 4k, it would be close...
by nettings
Sun Sep 24, 2017 2:13 am
Forum: Octo Sound Card for the Pi
Topic: Some measurements...
Replies: 8
Views: 6084

Re: Some measurements...

This is the noise spectrum, with the Micstasy gain at +18dB, so that a full-scale output produces a full-scale input to within maybe +/-2dB of error. I wonder what causes this... Could it be fixed with a more stable power supply? I'm using a five-way USB charger capable of delivering 2.5A on each ou...
by nettings
Sun Sep 24, 2017 2:05 am
Forum: Octo Sound Card for the Pi
Topic: Some measurements...
Replies: 8
Views: 6084

Re: Some measurements...

So I'm trying to quantify the noise floor by doing the following: I play an 1kHz sine wave through all eight Octo outs at -1.0dBFS into the eight Micstasy inputs. When I set them to +18dB gain, I get just about -1.0dbFS of peak value out of the AD converters. With this gain, I'm starting jnoisemeter...
by nettings
Sun Sep 24, 2017 12:40 am
Forum: Octo Sound Card for the Pi
Topic: JACK, DC signals, pinouts.
Replies: 7
Views: 3730

Re: JACK, DC signals, pinouts.

Hmm. The kernel driver thinks the card has 8 ins: static int audioinjector_octo_startup(struct snd_pcm_substream *substream) { struct snd_soc_pcm_runtime *rtd = substream->private_data; rtd->cpu_dai->driver->playback.channels_min = 8; rtd->cpu_dai->driver->playback.channels_max = 8; rtd->cpu_dai->dr...
by nettings
Sun Sep 24, 2017 12:00 am
Forum: Octo Sound Card for the Pi
Topic: Some measurements...
Replies: 8
Views: 6084

Re: Some measurements...

Having read about an Octo user who is using his in an analog synth context, I do understand the benefits of going down to DC... it's just that in everyday music use, DC coupling tends to cause quite a few problems if you're unaware of it, but hey, I take back my remark now that I've heard of a useca...
by nettings
Sat Sep 23, 2017 11:53 pm
Forum: Octo Sound Card for the Pi
Topic: Some measurements...
Replies: 8
Views: 6084

Re: Some measurements...

Here is a recording of output channels 5-8 playing digital silence. The noise peaks correspond to me running "ps aux" on the command line via an SSH session. You will notice that the noise level of channel 7 is also attenuated, not just the signal. Channels 1-4 look identical to 5,6 and 8. The wavef...
by nettings
Sat Sep 23, 2017 11:39 pm
Forum: Octo Sound Card for the Pi
Topic: JACK, DC signals, pinouts.
Replies: 7
Views: 3730

Re: JACK, DC signals, pinouts.

Using jack2 here without issues, and also a network audio connection with zita-njbridge (not netjack). All well, except somehow the card gets opened with 8 inputs rather than 6. Still investigating.
by nettings
Sat Sep 23, 2017 11:28 pm
Forum: Octo Sound Card for the Pi
Topic: sound quality
Replies: 5
Views: 2882

noise levels and high sample rates

Hi everyone, just a quick heads up: if you measure noise "by the book", you integrate across the entire spectrum. That means an excellent 192k device will have _four_times_ the noise of an excellent 48k device. If you want to read the same value always, you will have to use a bandpass from, say, 20 ...
by nettings
Sat Sep 23, 2017 10:43 pm
Forum: Octo Sound Card for the Pi
Topic: Purpose of P2 jumper on bottom of the board
Replies: 3
Views: 2548

Re: Purpose of P2 jumper on bottom of the board

Bump! I'd like to know, too!