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Raspberry PI Wolfson Audio card and ALSA

kjciszewski

I'm working with some code from an article "Introduction to Sound Programming with ALSA" from Linux Journal (http://www.linuxjournal.com/article/6735), from around 2004. It looked interesting, so I took the "listing3" and "listing4" files and compiled them (gcc filename.c -lasound).

 

I have a Wolfson audio card installed on a PI. I have been able to get the "listing4" recording program compiled and recording, and I can playback the "sound.raw" files created using the "aplay" scripts that Ragnar Jensen provided recently. Getting the "listing3" playback program to play back has all kinds of errors, mostly "underrun" errors. I did notice that the files played using the "aplay" scripts sounded faster (up-tempo) than the original recording.

 

I was wondering if anyone would take a look at this and see what might be going on.

 

Thanks!

 
Posts: 21
Joined: Sat Aug 11, 2012 2:20 pm

  

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  • 0

    Kenneth,

     

    Are you using a Class 10 SD card? I found that a good quality Class 4 card still caused stuttering on HD playback and underrun errors might be an indicator of low SD card data transfer. It would be unusual for playback software to slow down the tempo. If it did so, there would be a commensurate dropping in audio pitch. However, audio buffer underruns might leave many short silences which can be perceived as a slower tempo as the brain cannot 'hear' short silences.

     

    Roy Leith

  • 0 in reply to royleith

    The card is marked "10", so I think it is class 10.

     

     

    Do you know how the sampling rates for record and playback are set for the Wolfson device?  I did some testing--the card appears to support 44100, 48000, 96000, and 192000 codec rates, but nothing slower (using Ragnar Jensen's record and play scripts) in a loop around mode.

Reply Children
  • 0 in reply to kjciszewski

    I have the root file system mounted on hard drives or USB memory sticks on all my RPIs.

    I have seen the underrun errors when playing back from old, slow memory sticks.

     

    Class 10 cards are optimized for sequential reading and writing of very large files, i.e. video. They often don't work well for file systems with many small files, especially if the file system gets fragmented. Class 4 or 6 cards are many times a better choice.

     

    There is a bug in the Wolfson driver; sample rates below 32K are not supported. http://www.element14.com/community/message/107271/l/re-pjsippjsua-with-wolfson-audio-card#107271

    Usable sample rates are 32000, 44100, 48000, 88200, 96000, 176400 and 192000.

     

    I have tested "listing3". It works OK on my Pis, playing back from HDD.

    --

    Ragnar

  • 0 in reply to Former Member

    Thanks, Ragnar, for taking the time to investigate this.  What brand of HDD do you use?  I assume it's a USB type of some sort.

     

    I have a small USB hard drive from about three years ago (Verbatim AC320GB) that I might want to use for this purpose.  It's a FAT32 format when plugged into a Windows 7 machine.  I don't know (because I don't know a lot about Linux) what the required format for an HDD is for a PI running Raspian, so perhaps you could enlighten me.

     

    Is there information somewhere on how to mount the root file system on an HDD or USB stick?

     

    I apologize for asking so many questions, but I am not very far up the Linux learning curve, so I often need some help.  You a

    have been a great help.

     

    Thanks again.

  • 0 in reply to kjciszewski

    Thanks, Ragnar, for taking the time to investigate this. What brand of HDD do you use? I assume it's a USB type of some sort.

    I have more than a dozen different USB HDDs; Verbatim, Western Digital, LaCie... Also some generic enclosures together with USB to eSATA adapters and some USB/eSATA docking stations where I use drives from the small mountain of drives I have in the garage...image

     

     

     

    I have a small USB hard drive from about three years ago (Verbatim AC320GB) that I might want to use for this purpose.

    That one is bus powered (if it is this one) and that is where one might get into trouble. It gets its power from the USB socket. The RPi cannot supply the amount of current the drive needs from its USB ports, so the drive has to be connected through an USB hub that has its own power supply. Furthermore, some bus powered drives draw so much current that a single USB socket cannot cope. That can be remedied by using an USB Y cable to power the drive from two of the hub's USB ports. I have two drives, a Verbatim and a Western Digital, that need an Y cable.

     

    It's a FAT32 format when plugged into a Windows 7 machine. I don't know (because I don't know a lot about Linux) what the required format for an HDD is for a PI running Raspian, so perhaps you could enlighten me.

    ext2 or ext4 are the standard file system types in Linux. They are basically the same, the big difference being that ext4 has journaling that makes it more robust and more likely to survive a sudden crash. Journaling creates more writing activity though, so ext4 is often not used on memory cards. I use ext4 on all my RPi-connected HDDs.

     

     

    Is there information somewhere on how to mount the root file system on an HDD or USB stick?

    http://www.raspberrypi.org/forums/viewtopic.php?f=29&t=44177

     

     

    I apologize for asking so many questions, but I am not very far up the Linux learning curve, so I often need some help.

    No problem at all image

    --

    Ragnar