Raspberry Pi: More About Sound Recording
I’ve moved on to the official Raspbian release. This OS image using the hardware floating-point capabilities on board the RasPi and is noticeably faster than the Debian “squeeze” image was. It allows me to reboot when I’m powering the RasPi from my USB hub, something I couldn’t do before.
I’ve also tested a total of five different sound devices with Raspbian and ALSA for recording a mono microphone input. I’ve gotten one recording by fluke on a “Virtual 7.1 Ch Sound” device, and consistently get the claim that there is no capture device associated with the Behringer UCA202. The only device that has worked consistently for recording is a Syba “USB Stereo Sound Adapter” CMedia CM119. I didn’t pay more than $9 for any of the non-Behringer devices.
The CMedia is recognized, the controls come up appropriately in alsamixer, and arecord works without complaint on it. My only problem in simply going with this adapter is that I cannot reliably reboot my RasPi with it plugged into the USB hub. If it is plugged in on boot, the network interface throws “kevent 4” errors. If the network is not plugged in, but the CMedia device is, ALSA throws a lot of errors at boot. Given that I want to deploy my RasPi remotely for a couple of weeks at a time, this sort of behavior doesn’t give me confidence. Things have improved since the earliest firmware I was using, but there seems to be a ways to go.
Syba SD-CM-UAUD USB Stereo Audio Adapter, C-Media Chipset, RoHS ($8.08 from Amazon)
The currently non-recording adapters:
Virtual 5.1-surround USB 2.0 External Sound Card ($1.78 from Amazon)
7.1 Channel USB External Sound Card Audio Adapter ($2.38 from Amazon)
Behringer UCA202 ($29.99 from Amazon)
Intermittently working adapter (I can’t say exactly how I managed to get one recording done with this):
Syba USB2.0 7.1CH Sound Adapter Add Stereo Output Mono Input Led ($3.28 from Amazon)
A nasty workaround could be to switch power to the USB hub *after* the Raspberry boots. It is possible to control some of the I/O lines to drive a transistor (or latching relay) switch that in turn controls power to the hub.
I’ve got a BeagleBone but haven’t played much with audio. There was a blog entry about using that unit to record audio from a USB card here:
http://www.amelito.com/rec/livebone/en/
Could it be to do with power supplies?
My rPi boots and works fine off a micro-usb 5V 1A mains adapter from RS and has written to a single usb memory stick. I have doubts that its usb connector can provide the 5V 1A of the usb specification expected by your external sound devices. Measuring the voltage at a 1:7-way usb adapter, the rPi seemed to be providing a miserly 3V, which could adversely effect most usb devices.
A switch at the 7-way ceased to power this adapter from the rPi. Four NiCad rechargeable 2000mAh batteries powered this 7-way hub sufficiently for rPi Debian6 to find multiple usb memory sticks and copy >1GB from one to the other. This configuration with a separate 5V supply for usb devices might suit your applications.
Don’t use four non-rechargeable batteries as those would add up to 6V not 5V.
Please let me know if it works.
Yeah, I’ve been thinking of using an Arduino or Basic Stamp to control a couple of relays to control the RasPi bootup sequence. As you said, it seems a nasty solution, but at least it is a possible solution.
I’m working on getting mic input on my pi as well. Bought a SYBA card (on its way) and I want to use mine to do audio input for voice chat.
I’ll be putting my progress on my site here: http://andrewtjohnson.me/2014/07/proposed-project-raspberry-pi-usb-sound-card-interface/
Any trouble getting drivers installed for the SYBA? Be interested in any helps you have. Contact me: http://andrewtjohnson.me/contact/
Other than the Behringer, the issues I was having didn’t seem to relate to drivers.
I need to revisit this. Last time I tried, I was having some issues related to power. I think I may try a Model B+ and see if that helps.