[LAU] Raspberry Pi and real-time, low-latency audio

[Jeremy Jongepier]

On 04/17/2013 09:49 AM, Carlos sanchiavedraz wrote:
> 2013/4/15 Jeremy Jongepier <jeremy at autostatic.com>:
>> On 04/15/2013 10:39 AM, Carlos sanchiavedraz wrote:
>>>
>>> Just a USB cable from RPi to an A/C to USB adapter, and UA25EX
>>> connected direct to the USB on RPi.
>>
>>
>> Check the current of the adapter, if it's somewhere around 1A you might need
>> a more powerful adapter as the RPi already draws 700mA IIRC.
>
> The adapter is the same as that ones to charge mobile phones, just an
> adapter from USB to a switch. I thought it would be enough to plug the
> UA to the RPi and not having to plug it to an USB powered hub, because
> then it may occur problems with other devices plugged in it, and this
> would probably increase problems with audio latency and such.
>

I haven't had any problems with audio latency and using a powered hub.

>>
>>
>>> IIRC, when configuring using raspi-config, the Modest preset for
>>> overclocking just increases the CPU freq from 700MHz to 800MHz. I
>>> didn't want to risk my SD because I red that issue you mention, but it
>>> seems that anyway I've left without my SD.
>>>
>>
>> What kind of SD are you using? I've used different SD cards with different
>> results. I'm now using a cheap OEM class 10 SD card that does get corrupted
>> quickly but performance is better than other SD cards I've used. Whenever I
>> change something I make a backup now.
>
> I'm using a SanDisk 2GB microSD on a SD adapter for the RPi slot. I
> never had any problem until now.
>

And that while SanDisk SD's are being recommended for use with the RPi. 
What core_freq are you using?

> Do you still can use yours once it is corrupted? I plug it, you can
> see the two partitions  mounted for a moment but then it unmount
> itself. I made a backup copy with dd once I configured some
> parameters. I've and tried several times to transfer it to the SD with
> dd again but at about 840MB transfered it stops with a corruption
> error; I only can modify the scripts and config on the first partition
> (boot partition) when it stays mounted for some time.

First thing I do when a SD becomes corrupted is wipe all partitions and 
then restore an image with dd. If you run into corruption errors the SD 
might be defective?

>
> This could allow me to maybe boot a system in a USB stick, but then I
> waste one USB slot, and I'm afraid that if I buy another SD card it
> could be corrupted again and then it would be wasted money.

You can boot from an USB stick connected to a hub. I've tested this when 
trying to run a RT kernel on the RPi. But either my USB stick or the RPi 
itself has issues with the throughput because I had the idea the RPi was 
a lot less responsive and audio was completely distorted.

Jeremy