sbp wrote: 
> Hi thank you for working on this.
> 
> In order to find the name and control than can manipulate the card. You
> first will have to find out the number assigned to the IQaudIO card.
> I use this command:
> sudo cat /proc/asound/cards
> 
> 
> The IQaudIO is probably card 1. So next you can use this command:
> amixer -c 1 controls
> I think this is the command you should use. It will give you the info
> you need.
> 
> Whereas
> amixer -c 0 controls
> will probably show you the info for the analog ALSA card.
> 
> 
> Regards
> Steen

Thanks for the replies everyone. uname -r gives:

4.1.6-piCore+

amixer -c 1 controls gives:

numid=6,iface=MIXER,name='DSP Program'
numid=3,iface=MIXER,name='Analogue Playback Boost Volume'
numid=2,iface=MIXER,name='Analogue Playback Volume'
numid=10,iface=MIXER,name='Auto Mute Mono Switch'
numid=11,iface=MIXER,name='Auto Mute Switch'
numid=8,iface=MIXER,name='Auto Mute Time Left'
numid=9,iface=MIXER,name='Auto Mute Time Right'
numid=7,iface=MIXER,name='Clock Missing Period'
numid=5,iface=MIXER,name='Deemphasis Switch'
numid=4,iface=MIXER,name='Digital Playback Switch'
numid=1,iface=MIXER,name='Digital Playback Volume'
numid=20,iface=MIXER,name='Max Overclock DAC'
numid=19,iface=MIXER,name='Max Overclock DSP'
numid=18,iface=MIXER,name='Max Overclock PLL'
numid=16,iface=MIXER,name='Volume Ramp Down Emergency Rate'
numid=17,iface=MIXER,name='Volume Ramp Down Emergency Step'
numid=12,iface=MIXER,name='Volume Ramp Down Rate'
numid=13,iface=MIXER,name='Volume Ramp Down Step'
numid=14,iface=MIXER,name='Volume Ramp Up Rate'
numid=15,iface=MIXER,name='Volume Ramp Up Step'

I've tried both 'analogue playback volume' and 'digital playback volume'
but both give the error:

IQ_rot: simple.c:282: snd_mixer_selem_get_playback_volume_range:
Assertion `elem' failed.

which means they are the wrong label. The only label that has worked is
'PCM' but it doesn't change the volume despite the metered gain levels
changing.

To answer another question about why....Using LMS (I think) changes the
input level, which leads to a gain structure with less fidelity. As far
as I know, for digital processing or line level devices, the input gain
should be fixed and the volume increase based on amplifier gain rather
than input gain. My squeezebox has a fixed level that feeds a dac built
into my Moon amplifier and I use the amp's volume control. I used to be
able to do it via the IR blaster but that doesn't work any more. I want
to build a custom headphone amplifier with alarm clock etc., and I would
like to be able to control the volume on the box with a rotary encoder.
More for convenience than anything. Ultimately I'd like to build the
full functionality of the squeezebox, with song selection etc (also need
rotary encoders) and possibly some real analogue VU meters. Yes, I'm a
dreamer.


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