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Raspberry Pi and DACs

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Steve Conner

Wed Aug 01 2012, 10:47AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Would you care to qualify that by telling us what media player software is installed on it and whether it gives audio over HDMI?

Steve Conner

Wed Aug 01 2012, 01:38PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Sorry for the double post, but I think I answered my own question:

RaspMBC is a media centre distro and it appears to support digital audio out over HDMI.

Pinky's Brain

Wed Aug 01 2012, 03:36PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Then you need a HDMI to SPDIF converter ... kinda getting away from cheap and small.

Steve Conner

Wed Aug 01 2012, 09:52PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The cheapest one I could find cost $10 more than the RPi itself :(

Still, you have to weigh it against the cost of the time taken to write a driver for whatever codec chip you might choose. Or maybe RaspBMC could easily be modified to drive a USB DAC, if it doesn't do that already?

Ash Small

Sat Aug 04 2012, 11:51AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Here is a link to the 'multimedia' section on the RPi forum, which may be of some relevance here;

EDITED; SEE THE TWO POSTS BELOW

Pinky's Brain

Sat Aug 04 2012, 12:45PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Ash Small wrote ...
and HDMI-RCA converter for $8 from Amazon;

That's a scam :/

Ash Small

Sat Aug 04 2012, 01:40PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Pinky's Brain wrote ...

Ash Small wrote ...
and HDMI-RCA converter for $8 from Amazon;

That's a scam :/

So it is Pinky, I've just read the reviews. It looks lke you do need to spend ~$40.

Steve Conner

Fri Nov 23 2012, 08:36PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I decided to resurrect this thread, as I've built a fairly successful Pi-based music player.

I used a Raspberry Pi Model B, a Â£29 USB DAC from Maplin (order code A14KF) and a spare 300GB hard drive in an external USB enclosure.

Using the latest Debian Wheezy image, the DAC is recognised automatically by snd-usb-audio. Due to the Pi's slightly funky USB controller, it won't play at bit rates above 44.1k/16 bit without stuttering and interfering with the USB keyboard. I decided to continue as 99% of my music collection is in this format.

I installed mpd (the "Music Player Daemon") and ncmpc, the console-based interface for it. After making the console font bigger, this interface works nicely on a tiny Â£16 reversing camera monitor from Ebay, hooked up to the Pi's composite output. Due to the 44.1k/16 bit limitation, I set mpd to resample everything to this format using its highest quality setting.

So yeah, a 300GB player that supports lossless formats for under Â£100.

The Pi's main chip has an I2S output, and this is brought out to the GPIO pins. It would be really nice if someone would write an ALSA driver for it.

Some guys over at DIYAudio tried and failed, the DMA controller was too much for them:

Carbon_Rod

Sat Nov 24 2012, 02:37AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

@Steve
The Pis Audio & PWM DMA can be conflicted by device drivers.

#To enable the stereo analog line output:
sudo modprobe snd_bcm2835
sudo amixer cset numid=3 1

#Classic way to test audio:
sudo apt-get install flite
sudo flite -voice slt -t "The Enrichment Center is required to remind you that you will be baked, and then there will be cake"

Not sure about bit rates, but it plays fine with the most recent Wheezy kernel overclocked at 950MHz. Most Pi issues happen with a slightly unstable power supply, and it helps to have a 2A+ external 3.3v LDO regulator for DAC chips etc.

#Run kernel update
sudo raspi-config

#after script completes, re-run to overclock to "High" mode and set GPU to 16MiB
sudo raspi-config

#...reboot to enable the new settings

macona

Sun Nov 25 2012, 08:58AM

Registered Member #3272 Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101

Why not use a Teensy 3.0? It is an ARM cortex M4 with DSP functions at 48Mhz (Overclockable to 96) and can handle a I2S audio input. Native USB so you dont have to deal with a serial-USB bottleneck.

DPSS Yag laser cavity by macona, on Flickr

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