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How to avoid audio coupling between channels when designing a PCB?

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leolib2004

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Hi,

I am designing a device which will have to output audio to headphones. I have chosen the CS42L51 audio codec to do the work but I am concerned about audio coupling. I have a dev board (SAM V71 Xplained Ultra Evaluation Kit) where audio coupling occurs and it's something I can not stand. I have created an audio file using Audacity which only outputs sounds to the left channel and I also used this video: https://www.youtube.com/watch?v=hTvJoYnpeRQ in order to test this in my z1 compact phone, my mac book pro and an iPod Touch 6th gen. The results are that audio coupling also occurs on my phone, minimal compared to the dev board but it occurs.

How one can do a proper design to avoid that?
 

leolib2004 said:
Hi,

I am designing a device which will have to output audio to headphones. I have chosen the CS42L51 audio codec to do the work but I am concerned about audio coupling. I have a dev board (SAM V71 Xplained Ultra Evaluation Kit) where audio coupling occurs and it's something I can not stand. I have created an audio file using Audacity which only outputs sounds to the left channel and I also used this video: https://www.youtube.com/watch?v=hTvJoYnpeRQ in order to test this in my z1 compact phone, my mac book pro and an iPod Touch 6th gen. The results are that audio coupling also occurs on my phone, minimal compared to the dev board but it occurs.

How one can do a proper design to avoid that?
Click to expand...

At audio frequencies the PCB alone would not cause any crosstalk. Components and connections would. DC power lines also contribute.

When designing a PCB, separate the two or more audio channel lines and components as far as possible. Separate all connecting lines, for controls and mainly for DC power. Use large blocking capacitors. If needed, use metal sheet screens.
Be aware that signal sources can already be coupled before connecting to your device. Also output lines can couple when running close over a distance.

Check active component specifications for crosstalk data.
 

Keep all signal line impedances as low as possible, say below 10kΩ.
That will minimize the effect of stray capacitance coupling between channels.
 

I concur with jiripolivka. My emphasis: Watch out for shared impedances, particularly on power and ground. Many audio ICs put both channels in the same chip so you can't physically separate them. You want the power supply impedance at the audio ICs to be as low as possible. Use copper planes or short wide traces. Use lots of decoupling capacitance.

Make "return" path impedances as low as possible and separate the return currents where possible.
It is unfortunate that headphone connectors use a shared pin for return current. Good headphones will use a separate return wire for each channel.
 

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