remote controlled audio mixer/equalizer project


I would appreciate some suggestions for implementing a stand-alone audio mixer/equalizer box using commodity components, in the shortest development time at the least possible cost. I am tending to want to to use four PCI sound cards in an older PIII 1u rackmount cpu to create a four audio bus/eight inputs mixer, with four independent equalizer channels. It should be controllable using an arbitrary protocol over RS232 or ethernet, not require a resident GUI, nor local mass storage except perhaps flash for program loading, and won't do any local capture, only audio I/O at 44.1 or

48kHz sampling rate to and from unbalanced line level connections.

Some preliminary thoughts are to use a version of *IX as the o/s and layer ALSA and LADSPA with plugins on it, connected with the 'jack' framework, and for testing just control it through remote shell command scripts until a complete control program is written. Since I'm using low-end hardware, I had dismissed using 'Pulseaudio' as a framework (unless convinced otherwise).

Should I be considering some other o/s or RTOS?

Has this been done as an opensource or freeware project (I don't find much on the 'net)?

Replies are much appreciated.


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Why do you want to do this rather than use an existing device that does this? There are a bunch of devices like this out there, including a popular one from Roland that is well-documented.

If I were doing something like this and I were having to use generic PC hardware, I would consider RTLINUX. It would be different if the PC were just a front end to a dsp, though.


"C'est un Nagra.  C'est suisse, et tres, tres precis."
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Scott Dorsey

PCDJ will let you controll multiple outputs, not sure if it had a remote function - but it can be controlled via keyboard short cuts and I have seen somewhere a keyboard rs232 interface so that a dumb terminal can be used as a keyboard on a remote machine bit like a remote KVM. There are also KVM's via ethernet about.

thoughts about your hardware - can you get four PCI cards in a 1u rack, is there physically enough space ?

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Acquisition cost - I need to make several of these and can't afford commercial versions.

Thanks - I'll look at RTLINUX.

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I have a few M/B choices that permit four PCI sound devices in 1u; the first is three PCI cards and one integrated audio chipset, the other is a low-profile riser PCI bus with dual opposing slots (four slots).


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Are the four cards locked together via spdif or workclock?

I don't think jack will work nicely (easily) with four separate sound cards. It definitely won't if they are not locked together. You could run a separate jackd server for each card, I suppose.

I wouldn't use Pulseaudio either.

What kind of latency is acceptable? What standards of reliability? (Will you lose your job if it breaks? ).

I'd use PureData with straight forward ALSA. It can interface with virtually anything and will run headless perfectly happily. It's great for rapid prototyping of audio ideas.

Also, have a look at Faust.

I think a Linux Music distro like 64Studio would be easier than a RTLinux or other *nix. Otherwise you will spend all your time compiling obscure libraries and messing about just to replicate the work others have already done.

Linux-audio-users/dev mailing lists would be a good place to ask.

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Thanks for the heads-up; I had not considered creating a single virtual sound device but only a 'jackd' per card. I found considerable discussion of this topic on the web, for example a good overview:

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If I combine the cards, I'll distribute one hardware clock to all of them. In your view, what advantages are there to combining them for my application?

On the order of 10ms as I currently see it.

Should be stable for up to four hours ;)

Interesting, sort of an audio LabView... You are suggesting controlling my remote audio processor in an X-window?

Indeed, I am guilty of tending to do the latter. For the use of old hardware as I intend, what kernel version would you recommend? I have preferred

2.4.27-xxx in the past.



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Can you post a link to these options. I have had occasions in the past where I needed to fit a "standard" PC into odd enclosures, and having links to these type of products is always helpful.

Regards Anton Erasmus

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Anton Erasmus

As a rabid proponent of reuse most of my projects are based upon salvaged items; in this case I have a selection of custom mainboards and chassis from various old IP firewalls, compression protocol accelerators, industrial controllers, etc., which stand only a remote chance of appearing on auction or recycle sites. If you still want data, I can poke at them for model and ID information later on ;)

N.B. some time back I began a list of salvage items that contained reusable FPGAs and posted it with a few updates to the newsgroups but that effort produced mostly disinterest.


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