I have a few more SD cards on the way (some from the hardware-compat list). Will see if it sorts it. The one in question now is a Sandisk Extreme III 8GB.If you have any suspicions about the SD card then change it
Fortunately (or unfortunately depending on your perspective)... I already owned the Firestone gear. It's my primary DAC for my home system (and sometimes at my desk when I'd otherwise piss off the neighbors). No "additional" expense for this rpi-hackery. (this time). The onboard analog just wasn't gonna cut it, mostly because of the experimental driver "thumpyness on init" that is mentioned elsewhere. Not about to subject my systems (or my ears) to that glitch.There are cheaper ones than the Firestone
Have you tried higher frequency files? Everything with frequencies > 44.1kHz produce audible crackles and drop outs. I think the USB of the Pi can deliver the frames fast / steady enough.jetblackstar wrote:Ok,
I'm retracting various conjecture about the shielding and isolation of the Pi.
Combining knowledge gleaned from posts by Dom on the inbuilt soundcard (regarding sound glitches) I've discovered the audio interference is mostly software related.
Thanks to a post here:
http://www.raspberrypi.org/phpBB3/viewt ... =38&t=7000
I found how to force ALSA to use the Wolfson hardware DAC in the i-Basso.
I had to change his entry in the asound.conf to make card 1 default So be warned you need to check which number it is with amixer or alsamixer first.
But after that I've got some seriously lush sound beaming out. As of yet no dropouts, no fuzz. Lovely sound.
If your USB soundcard can possibly support the hardware setting I suggest it. I have a suspicion not all of them can.
I'll go and find an old Creative USB soundcard we've got, which would include infrared and mic input for those above that want to record. See if that works well.
So first time pi boot on Debian breezy, after the basic wander round the capabilities my first instinct was the sound.
I'm a bit of an audiophile and the idea of a Linux music player outputting to a USB DAC smells of audio heaven.
First off to contribute; Person above experiencing odd gaps in audio. This is a normal phenomenon for USB audio. Usually happens then the audo device looses I/O priority to something else the CPU is doing. Or the PC player is struggling to produce audio at a consistent rate.
This seems very likely with the Pi and I'm glad you at least got mostly good audio.
It can be resolved by a newish technique called A-Synchronous USB audio. Something which is part of the USB audio DAC itself. Generally only found on hi end audio gear. In laymans terms are the audio device demands the highest priority with the USB I/O preventing dropouts and gaps.
There may be other ways to resolve the issue too, "nice" is one of them.
So first attempt was iBasso D-zero portable DAC/Amp (interestingly similar size profile as the pi and would stack together wonderfully). It massively exceeds the Pi in cost (weights in at £80 or $109), but there are more cost effective audiophile DAC amps out there (eg Fiio).
Instant recognition by the kernel and alsa. Woot. Given the inbuilt broadcom sound is disable by default it just worked. It deliberately has no volume control as it's fixed and you alter via the inbuilt amp in the d-zero case. So all apps happy. MP3 played but with some buzzing.
However I'm definitely picking up the same electronic interference others have reported. Mouse, and other actions give clear interference too. I'm hoping a new powersupply might reduce the background noise, but there does seem to be no isolation of the power output for the USB.
I've tried my Musical Fidelity V-Link SPDIF converter as well, which is a 24/96 bit device and as previously mentioned an A-Syncronous device. But the Pi freaked out trying to initialise it. A few message in the logs showing it couldn't give the device priority. So probably the Async bit thats borked.
I'm going to get a hub, perhaps a powered one. That might help iscolate noise, or possibly make it worse. Who knows.
Failing that I'm wondering about any DC battery projects to give cleaner power.
Or a separate power supply for the DAC.
Will keep you lot updated.
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