Re: MAN301 internal routing (Re: [PATCH] ALSA: dice: add stream format parameters for Weiss devices)

[Takashi Sakamoto <o-takashi@sakamocchi.jp>]

Hi Rolf and Michele,

On Wed, Feb 28, 2024 at 09:32:45AM +0100, Rolf Anderegg wrote:
> Hi again, quick followup:
> So basically it's like this:
> 
> ```
> spdif-opt-input-1/2  ---+
> spdif-coax-input-1/2 --(or)--> digital-input-1/2 -----------------> stream-output-1/2
> aesebu-xlr-input-1/2 ---+
> muted ------------------+
> 
> stream-input-1/2 --------------------------+----------------------> spdif-coax-output-1/2
>                                            +----------------------> aesebu-xlr-output-1/2
>                                            +--analog-output-1/2 --> analog-xlr-output-1/2
>                                                         +-----------> analog-coax-output-1/2
> ```
> 
> And all potential mixing (e.g. volume processing) would be done in userspace on the firewire host.
>
> On 28.02.24 09:14, Rolf Anderegg wrote:
> > On 28.02.24 00:54, Takashi Sakamoto wrote:
> > > [...]
> > > 
> > > I assume that the actual source selection of 'digital-input-1/2' is done
> > > in the router function of DICE chip as well as the selection between
> > > 'digital-input-1/2' and 'stream-input-1/2'. The mixer function of the
> > > chip is not used as I expected, thus the selection should exist as the
> > > source of audio signals for the outputs. However, in the above description,
> > > I cannot find such selection.
> > > 
> > > Or the device has a fixed route between 'stream-input-1/2' and
> > > 'analog-{xlr,coax}-output-1/2'? The user can not hear the audio signal
> > > of opt/coax/xlr digital input ports in the analog outputs?
> 
> Exactly, this is fixed as you can see in our DICE routing method.

Ah... OK, now I got it. I had assumed that the audio signal to any
digital input interface can be dynamically routed to any of the audio
output according to the preference selection, however it is not. Unlike
the equipments for the studio recording, the feature so-called as 'direct
monitoring' (without multiplexing) is not implemented in MAN301. As a
summary, the captured digital audio signal has the long trip to user's ear,
like:

```
spdif-opt-input-1/2  --+
spdif-coax-input-1/2 -(or)--> digital-input-1/2 ---------------> stream-output-1/2
aesebu-xlr-input-1/2 --+                                                  |
muted -----------------+                                                  |
                                                                          |
(Linux system)                                                            v
pcm-playback-1/2 <------ (software digital audio processing) <-- pcm-capture-1/2
       |
       v
stream-input-1/2 -------------------------+--------------------> spdif-coax-output-1/2
                                          +--------------------> aesebu-xlr-output-1/2
                                          +-analog-output-1/2 -> analog-xlr-output-1/2
                                                    +----------> analog-coax-output-1/2
```

I've already uploaded `firewire-dice-protocols` crate v0.3.0 to crates.io
with the diagram including the selection[1], but it should be fixed. I'll
do it later.


Thanks

[1] https://docs.rs/firewire-dice-protocols/latest/firewire_dice_protocols/weiss/avc/index.html

Takashi Sakamoto