USB audio clicking and popping - diyAudio
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Old 11th August 2014, 05:45 AM   #1
hjf is offline hjf  Argentina
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Join Date: Dec 2010
Default USB audio clicking and popping

Just for fun, I built the circuit in the TPA6120A2 datasheet: a PCM1792 DAC, a quad opamp, and the TPA. As a source for the PCM i used an USB-I2S IC, the Silabs CP2114.

It's a nightmare!

For some reason, I get clicking noises all the time. Sometimes that clicking is once every 2-3 seconds. Sometimes it's 3-4 times per second. And it's LOUD!!

What can be the problem here?
Here's a capture of the clicking:
Click the image to open in full size.
As you can see, after the clicking there is a HUGE spike (enough to make your ears ring).
This only happens when sound is playing. When I stop the music, I2S data stops, and noise too. If I mute the DAC (via software, enable attenuator at -120dB), I can still hear the clicking.
The problem happens in 3 different machines (Core2duo laptop, Core i5 desktop and an old athlon64).
I've tried setting a higher USB audio buffer. I also tried using an ASIO driver.
Changing USB ports doesn't help either (Neither my USB2 or USB3 ports make a difference).
Is the CP2114 just a bad USB-I2S bridge? Is it a windows problem?
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Old 11th August 2014, 12:26 PM   #2
marce is offline marce  United Kingdom
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Location: Blackburn, Lancs
layout etc would help.
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Old 11th August 2014, 02:08 PM   #3
hjf is offline hjf  Argentina
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Well, it's not that I'm very proud of my laoyut, but here it goes.

Click the image to open in full size.

Board on the left is the USB-I2S chip, on the right there's the DAC board, I/V stage, and audio amplifier.

Pay no attention to the 46MHz oscillator. This has been replaced with a 48MHz one. This board runs off two oscillators: an external one at 48MHz for USB, and the CP2114's internal oscillator running at 49.152MHz (Fs=48KHz * 256).


I doubt this is a layout issue since the popping is regular, not random.
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Old 11th August 2014, 02:47 PM   #4
marce is offline marce  United Kingdom
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Join Date: Jun 2007
Location: Blackburn, Lancs
For these sort of designs you need at least a 2 layer board with one layer being an contiguous ground plane, same for the wiring between the boards, each signal needs a ground return in intimate proximity and the next pin on the PCB.
The clicking is related to some data being fed to the board, and I suspect some sort of EMC problem, where a clock or a data line is coupling to some other input/output and causing the problem.
The way that clock is connected is possibly the worse thing you could do for a clock or oscillator, the clock signal should be as short as possible, same with the power leads and add some decoupling. Same with the IC's there is no effective decoupling on any of the devices, again this wont help. The caps need to be next to the pins not on some skinny traces a few mm away.

Last edited by marce; 11th August 2014 at 02:51 PM.
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Old 12th August 2014, 03:20 AM   #5
hjf is offline hjf  Argentina
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Join Date: Dec 2010
I tried this in Linux. It worked perfectly. No dropouts, no issues at all. Playing a wav of sinewave showed a perfect sine on my scope.
I guess it's something with Windows.
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