About the noise

Sub forums for various specialist XMOS applications. e.g. USB audio, motor control and robotics.
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sm2413
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Joined: Tue Sep 10, 2013 5:17 pm

About the noise

Post by sm2413 »

Hi, I have two Digital to Digital Converters(USB to SPDIF) which are equipped with Xmos chip. I connected them to my PC & DAC. The protective relay of the digital input on my DAC always trigger when the sampling rate have been changed. I would like to ask a few questions:

- Is it true that Xmos chip don't respond to sampling frequency changes when the interface is active?
- Is a reset necessary for the chip after changing sampling rate?
- Is the shock(noise?) occur every time after the reset?
- Is there any idea to improve the problem of the shock(noise?)?

Thanks


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lilltroll
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Location: Sweden, Eskilstuna

Post by lilltroll »

the shock-noise - do you mean the behaviour of the DAC-chip during reset and maybe Power on/Power off ?? Probably a DC-pop ?

One way to cope with problems with power on/power off/reset is to insert a relay on the output, between the DAC and the lineout, controlled by the XMOS chip. By default the relay should be in a non conducting state during power on etc.
An cheaper solution is to use a FET in a shunt configuration on the lineout.
During mute it will shunt the output down to ground, and when everything is stable and the mute is released the FET will be put in a non conducting state. There is many variations on this transistor based solution.
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Ross
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Location: Bristol, UK

Post by Ross »

sm2413 wrote: - Is it true that Xmos chip don't respond to sampling frequency changes when the interface is active?
The XMOS device will always respond to sample frequency change requests from the host
sm2413 wrote: - Is a reset necessary for the chip after changing sampling rate?
No it doesn't.

Please note the above assumes the reference design in its default state. Someone could have changed the code to do both of these things.
sm2413 wrote: - Is the shock(noise?) occur every time after the reset?
- Is there any idea to improve the problem of the shock(noise?)?
I'm afraid I don't understand these questions. Please note this is forum for people developing with XMOS devices. If you have an issue with an XMOS based product you should contact your vendor.
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Ross
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Joined: Thu Dec 10, 2009 9:20 pm
Location: Bristol, UK

Post by Ross »

lilltroll wrote:the shock-noise - do you mean the behaviour of the DAC-chip during reset and maybe Power on/Power off ?? Probably a DC-pop ?

One way to cope with problems with power on/power off/reset is to insert a relay on the output, between the DAC and the lineout, controlled by the XMOS chip. By default the relay should be in a non conducting state during power on etc.
An cheaper solution is to use a FET in a shunt configuration on the lineout.
During mute it will shunt the output down to ground, and when everything is stable and the mute is released the FET will be put in a non conducting state. There is many variations on this transistor based solution.
I think the unit is USB -> SPDIF. I guess the DAC on the other end of the SPDIF cable is generating a noise when the stream is lost during rate change.
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