Transferring audio by I2S

Thread Starter

Marcel DaJanchar

Joined Sep 9, 2015
32
Hello!

My plan is to create a circuit, which would effectively transfer 6 channels of analog 16-bit audio signal to the other side without loosing quality or inducing some kind of interference. Cable length would be around 5 meters. This circuit would be used in automotive to substitute 6 RCA cables going from car headunit to the amplifiers in the back. Right now, RCA cables are too thick and takes too much space. Also due to their wiring, some interference occurs as they are wired next to the power wires of the car existing wires.

The main stages of the circuit would consist of converting analog to I2S signal, sending the digital signal down the line and on the other end converting I2S signal to analog again (using DAC). Block scheme can be seen in the attachement. The main issue I have is the transfer path itself. I want to minimize the number of wires in the cable, so some kind of TDM would be performed. I was thinking about using a multiplexer which would switch between 6 channels every 16th clock pulse of I2S. That way, I would convert six I2S frames into one longer chain of frames. This frame would be then transferred through some high-speed cable (was thinking CAT5) on the other side. At the other side, a demux would switch between each DAC channel and 'write' the appropriate I2S frame on them. I suppose there would be some timing delay present as frames cannot be sent in parallel, so little buffering should be considered.

So my questions are the following:
1. Is this concept overengineered and can be solved by using some kind of IC which does all that internally? I was looking at ADAU7118 IC to replace the input stage, but I cannot find the way to convert analog voltage to PDM signal.

2. Is CAT5 cable suitable for this kind of frequency? I suppose that sampling frequency would be 44.1kHz * 16-bit * 6 channels = 4.237 MHz. Is my assumptions correct?

3. Can I2S signal be transferred over this kind of distance? Should I use LVDS to transfer the data over the wire?

Any help would be appritiated. Thanks!
 

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MrChips

Joined Oct 2, 2009
31,083
Just thinking about this, I would not use I2S. I would send UART data over RS-485 or fibre-optic. RS-485 needs a single twisted pair. Fibre-optic cable is even thinner and suffers no interference.

You don’t need a multiplexer. The data is encoded with additional bits to identify channels.
 

Ian0

Joined Aug 7, 2020
10,276
Convert it to S/PDIF (there are ICs that do it - WM8804, etc) then you can send it transformer coupled, by RS485, or even by fibre-optic.
One IC will do four channels.
Twisted pair will easily manage it over 5m.
A really good quality amplifier may even have an S/PDIF input.
 
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