Re: Implementing digital crossover?

[Takashi Iwai <tiwai@suse.de>]

At Mon, 20 Oct 2003 09:35:57 +0200,
Svante Eriksson wrote:
> 
> Hi all,
> 
> What would be an appropriate ALSA way of implementing a two-way
> digital crossover PCM output?  What I would like is for an ALSA PCM
> device to provide two SPDIF outputs with high- and low-band audio for
> the left and right channels, respectively.  I'd like for this to be
> transparent to the applications that produce audio output.
> 
> Ideally, I would like for the filter parameters to be run-time
> tweakable, at least initially.  Would it be possible to use a
> mixer-like control interface for this?
 
we're considering user-defined controls which can be created/used
dynamically by user apps.  not implemented yet, thought.

> Similar to the filter parameters, I would like to control an external
> analog attenuator using an ALSA mixer control (likely through the
> parallel port).
> 
> Also, would using two different SPDIF output cards be too bad even for
> a proof-of-concept setup?  I'm considering adding another el-cheapo
> CMI8738 based card, but don't know how much the lack of
> synchronization will impact.  Has anyone got experience from this?  Or
> is it possible to synchronize two cards (possibly by hw modification)?

if you use two different type of cards, there might significant timing
delays.  on software level, you can link two streams so that they can
be operated (almost) simultaneously.
but the real situation is quite hardware specific...

> For a real setup, what is a good PCI-based 4-ch 2xSPDIF output card
> that has good ALSA support?  It should at least be capable of both
> 48kHz and 44.1kHz output (w/o hw resampling).  (Support for 24-bit @
> 96kHz would be appreciated as well.)

for example, the ice1724 boards can be linked on hardware, so you can
get the exact synchronization.
from the perspective of costs, cmipci is the cheapest, but there is no
guarantee that two cards can run parallel in sync.


Takashi


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