Search found 20 matches

by nettings
Sun Sep 24, 2017 2:13 am
Forum: Octo Sound Card for the Pi
Topic: Some measurements...
Replies: 8
Views: 4891

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: 4891

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: 2719

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: 4891

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: 4891

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: 2719

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: 2166

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: 2078

Re: Purpose of P2 jumper on bottom of the board

Bump! I'd like to know, too!
by nettings
Sat Sep 23, 2017 10:39 pm
Forum: Octo Sound Card for the Pi
Topic: Some measurements...
Replies: 8
Views: 4891

Some measurements...

Hi Matt, first of all, congrats for pulling this off - I still have no clue how you are piping this many channels through a single I²S bus! I ordered two RCA Octos from Amazon UK and I'm now measuring them. For "consumer" sound, they are pretty ok, but for professional use, there appear to be number...
by nettings
Sat Sep 23, 2017 7:35 am
Forum: Octo Sound Card for the Pi
Topic: Octo Sound Card attenuated output
Replies: 7
Views: 3916

Re: Octo Sound Card attenuated output

Same here. Channel 7 is about 11 dB down. Just running some measurements, will report back later.