Setting Up The USB Audio 2.0 MC Dev Board as a Matrix Mixer

[markgtr813]

I am working on setting up the XMOS USB MC 2.0 as a matrix mixer - i.e. all inputs are mixed to all outputs as:

CodeCogsEqn.gif

where out1 is the physical hardware jack OUT1 and USB1 is the output audio from a PC on USB channel 1.

The routing setup will be performed within the code - as opposed to using the supplied PC command-line host mixer control. The node mix levels (c11 - c88) will then be set dynamically (externally controlled).

I am trying to figure out the correct c_mix_ctl commands to send to the mixer to accomplish this. I should note that the c_mix_ctl chanend has been disconnected from Endpoint0 and connected elsewhere for this purpose.

I have figured out that the following code adjusts the physical OUT1/2 volume which, on the default setup, corresponds to USB Audio out channels 1 and 2:

Code: Select all

outuint(c_mix_ctl, SET_MIX_OUT_VOL);
outuint(c_mix_ctl, 0);
outuint(c_mix_ctl, desiredVol);
outct(c_mix_ctl, XS1_CT_END);

outuint(c_mix_ctl, SET_MIX_OUT_VOL);
outuint(c_mix_ctl, 1);
outuint(c_mix_ctl, desiredVol);
outct(c_mix_ctl, XS1_CT_END);

Now I am thinking that I can use similar code to set up the matrix routing (SET_MIX_MAP ?)and also control mixer node levels (SET_MIX_MULT ?). If this is correct, can someone advise on how this is done in code? If I am barking up the wrong tree, can someone advise on the proper way of accomplishing my goal?

Thank you in advance.

[markgtr813]

One week with no reply...

Is there a way to get in touch with an XMOS Field Application Engineer or audio product specialist? Unfortunately it seems that no support is offered in the forums!

Thanks

[Ross]

Hi there,

mix_map is the mapping of an channel into a input of a mixer (this can be USB channel or a physical audio channel)

[markgtr813]

Hi there,

mix_map is the mapping of an channel into a input of a mixer (this can be USB channel or a physical audio channel)

So are you saying that I should use the SET_MIX_MAP as:

Code: Select all

outuint(c_mix_ctl, SET_MIX_MAP);
outuint(c_mix_ctl, ?? what goes here ??);     //mix
outuint(c_mix_ctl, ?? what goes here ??);     //index
outuint(c_mix_ctl, ?? what goes here ??);     //val
outct(c_mix_ctl, XS1_CT_END);

If so, what do the 'mix', 'index', and 'val' integers represent?

What do the integers in the mix_map variable represent? I see the from the definition that the mix_map is an 8x18 array

Code: Select all

int mix_map[MAX_MIX_COUNT][MIX_INPUTS];     //makes an 8x18 array 

and I also see how the mix_map is filled

Code: Select all

case SET_MIX_MAP:
     mix = inuint(c_mix_ctl);
     index = inuint(c_mix_ctl); /* mixer input */
     val = inuint(c_mix_ctl);   /* source */
     inct(c_mix_ctl);

...
asm("stw %0, %1[%2]"::"r"(val),"r"(mix_map[mix]),"r"(index));

but it is still unclear to me what values I should be setting in the mix_map so that a matrix mixer is made.

Two further questions on the matter:
Where are the eight mixes output to? For example, where does mix 0 show up on the hardware connections

What are the numberings for the audio channels in MIX_INPUTS. For example, which MIX_INPUT is USB audio out 1?

[markgtr813]

Ross,

Can you offer me any more assistance in the areas that I have mentioned in my last post? I still need clarification on this topic. Thanks.

[Ross]

There are MAX_MIX_COUNT separate mixes (8 by default) Each of these mixs can have MIX_INPUTS inputs.

It sounds like you only require one mix?