[alsa-devel] M-Audio Fast Track Ultra (8r) mixer: How to verify dB information?

[Felix Homann]

Hi Clemens,


Am 10.09.2010 09:18, schrieb Clemens Ladisch:
> I'm using the mixer_vol_tlv TLV
>> callback right now but I'm not sure it produces correct data.
>>      
> Try alsamixer.  Or just post the output of "amixer contents" here.
>
>    

Well, according to alsamixer the mixer values are mapped to a range from 
0 to -128 dB.

'amixer contents' show entries of the form

     numid=112,iface=MIXER,name='DIn8 - Out7 Playback Volume'
       ; type=INTEGER,access=rw---R--,values=1,min=0,max=32768,step=0
       : values=-32768
       | unk-4-0xffffce00,0x00000000,

(numid and name changing of xourse for each control ).

Here are some examples of setting values with amixer:

     :~$ amixer -c 2 cset numid=1 50%
     numid=1,iface=MIXER,name='AIn1 - Out1 Playback Volume'
       ; type=INTEGER,access=rw---R--,values=1,min=0,max=32768,step=0
       : values=16384
       | unk-4-0xffffce00,0x00000000,

     :~$ amixer -c 2 cset numid=1 80%
     numid=1,iface=MIXER,name='AIn1 - Out1 Playback Volume'
       ; type=INTEGER,access=rw---R--,values=1,min=0,max=32768,step=0
       : values=26215
       | unk-4-0xffffce00,0x00000000,


     :~$ amixer -c 2 cset numid=1 100%
     numid=1,iface=MIXER,name='AIn1 - Out1 Playback Volume'
       ; type=INTEGER,access=rw---R--,values=1,min=0,max=32768,step=0
       : values=32768
       | unk-4-0xffffce00,0x00000000,


cat /proc/asound/F8R/usbmixer gives lines like this:

   Unit: 5
     Control: name="DIn8 - Out7 Playback Volume", index=0
     Info: id=5, control=7, cmask=0x8000, channels=1, type="S16"
     Volume: min=-32768, max=0, dBmin=-12800, dBmax=0

How do I tell the controls value range is correctly mapped to the dB values?

Kind regards,

Felix