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I'm having a hard time trying to understand some basic sound engineering concepts.

From https://en.wikipedia.org/wiki/Original_Chip_Set#Paula:

Paula has four DMA-driven 8-bit PCM sample sound channels. Two sound channels are mixed into the left audio output, and the other two are mixed into the right output, producing stereo audio output. The only supported hardware sample format is signed linear 8-bit two's complement. Each sound channel has an independent frequency and a 6-bit volume control (64 levels). Internally, the audio hardware is implemented by four state machines, each having eight different states.

How can these 4 input channels be translated into the modern DSP world? The only reference I can find when trying to google some modern DACs, is that they can support > 2 output channels (5.1 sound and so on). From what I understand, today the mixing is mostly done in software, and the combined result is then fed to the CODEC/DAC. Are there any analog mixer chips with multichannel support and how would they work?

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closed as unclear what you're asking by Chris Stratton, Dwayne Reid, Edgar Brown, Voltage Spike, Sparky256 Dec 23 '18 at 0:57

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ Sorry, but your question isn't very clear. Mixing is addition, possibly after scaling and possibly in select cases followed by limiting or compression where the trade-off of distortion is acceptable. But your 8-bit example is foreign to consumer audio uses like the 5.1 surround you mention - it is extremely low fidelity and would only be found in something like a VOIP chat. If you wanted to mix this in a conventional programming language you would first scale each by its level into at least a 16-bit word (probably larger or floating point) before adding. \$\endgroup\$ – Chris Stratton Dec 17 '18 at 17:19
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Paula was pretty nice but she had a tiny brain:

enter image description here

This chip pretty much had to have one DAC per channel plus analog mixing and volume control after the DACs, as when mixing digitally, every time you lower the volume of a channel by 6dB, one bit falls off at the LSB end. On a 24-bit DAC that's okay, but on a 8-bit DAC you really can't afford to lose bits.

How these 4 input channels can be translated into modern DSP world?

These days mixing would be done digitally before sending the data to the DAC, and we'd have one DAC per output channel (ie, per loudspeaker).

Is there any analog mixer chips with multichannel support and how it would work?

Sure, you could combine integrated analog pots to make something like a mixing console. Or use a real mixing console.

Pretty much the only reason to do this these days would be for musicians, to hear yourself playing without the latency of an ADC - DAC conversion. This requires a direct analog path between input to output, and analog mixing with the soundcard output if you want to play over a recorded track.

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This is pretty much how modern sound cards work:

Following the description, Paula simply gets audio as PCM samples, like those stored in an (uncompressed) .wav file.

So, there's nothing inherently different to "modern" audio hardware.

How these 4 input channels can be translated into modern DSP world?

Whilst not necessary, many higher-end modern sound cards do support some form of hardware mixing.

Is there any analog mixer chips with multichannel support and how it would work?

An analog audio mixer is really just a (weighted) signal adder and can be built with any opamp and a low amount of external resistors.

You could control multiple programmable-gain amplifiers and use the adder to mix the result, but that'd be a waste of money; you'd just do the mixing (and that is really just addition) in digital domain wherever possible.

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