Multiplexing and mixing

Something like this. There may be a dsp that will do the job. You do need to add a register for each input channel level at each output. If you want analog output you need some dacs. You need all of the inputs on each processor. The number of outputs on each processor is limited by processing speed.A regular processor could also be used but would probably be severely limited as to the number of inputs. You could also build a microsequencer to run the system.

Bob

I guess it would help if I posted the diagram.

Bob

This is the domain of sound programs (like Logic Pro on a Macintosh). Smaller numbers of channels are do-able with the nearly-free software, like GarageBand and iDVD.

Ahh, you don't want to use a standard audio encoding. If your samples are all the same, it's easier than if they aren't, but you WILL have to reinvent the wheel. It'll be harder if you insist on 'using discrete' than if you stick with massproduced computing machinery.

If it were an analog signal, you could buffer all the inputs with high output impedance gain-controlled amplifiers (LM13700 is a dual of one such amp), and just connect all the outputs together (which is allowed because they have high output impedance). The 'control' function would then just be generating slow waveforms to program all the gain-control pins, which is relatively easy.

Onto what sort of a channel do you wish to multiplex these signals? Something like USB, or the now-obsolete IEEE-1394/Firewire, to go from a box to a PC? Something like RocketIO to go from one chip to another on a board, or between two closely-spaced boards inside a box? A transcontinental cable?

You're talking about enough logic content that doing it with discretes would be huge, troublesome and expensive; depending on the nature of your channel and what you _really_ want to accomplish this would be a routine to moderately difficult job using FPGAs or DSPs.

This is an embedded solution and does not work with a pc or similar device. Because it is actually a mixture of digital and analog I need some way to pass around signals easily as I do not want to hardwire the signal chain.

Another method would be to have a central unit that had a buffer where each memory "slot" would correspond to an audio sample. The unit could dish out and update the buffer for all the modules. The problem is that each module would use a dedicated line and most lines would not be using much of the bandwidth available. The main problem is routing as it is much easier to have a bus. But since all the audio samples, given an instant in time, should be available it seems natural to stick them all on one wire.

I believe I can reduce the complexity by not mixing the signals at each step but have a "mixer" module. The problem here is that the number of audio slots needed will probably increase dramatically and I'll need more than one wire or use a high clock.

Routing and mixing are two different problems. Routing the TDM signals is trivial, mixing is much more complex.

Use a digital audio processor such as TAS3103. It has a bunch of digital inputs and outputs. You can route and mix the signals in all kinds of combinations. You can also connect several DAPs to multiply the number of channels. This is likely to be simpler and cheaper then any DSP or FPGA solution.

Completely impractical.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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At which point the method of choice becomes a PC embed. Something like PC104. There is sufficient processing power, USB interface support (for the digitizers and optional DACs), and a minimal OS and carefully tuned interface and you are golden. If you include GPL portions be careful of the licenses and clearly segregate which is your stuff and which is GPL. Commercial OS and SW licenses can kill you on cost (per unit) instead.