Media clock server causing noise

Sub forums for various specialist XMOS applications. e.g. USB audio, motor control and robotics.
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Joined: Fri Nov 17, 2017 8:59 am

Media clock server causing noise

Post by aerol »

I am building a Linux server talking and listening to xCORE™-200 AVB capable boards based on the XK-AUDIO-216-MC Multichannel Audio Platform. The boards contain an almost exact copy of the Multichannel Audio Platform boards. They all have 8 channel inputs and 8 channel outputs. The Linux server has Debian 10 and uses the LinuxPTP (v3.0), OpenAvnu mrpd, OpenAvnu maap_daemon and OpenAvnu 1722 packet format library for implementing the AVB stack. linuxPTP helps server's system clock to be synchronized to the ptp clock, whose master is an avb capable netgear switch. The boards run a slightly modified version of the XMOS sample application "AN00202_gige_avb_i2s_demo". 8 channel class A streams flow between the server and the boards. Apart from a few glitches the system runs fine with 4 boards connected to a single server. However there is one very annoying glitch related to the media clock servers on the XMOS boards. As soon as the media clock server locks on the server's talker stream a very strange noise starts on input channels 0 and 1 on the board. The input to the boards are highly amplified microphone signals so they are already a little bit noisy but not like the way when the media clock locks on. The noise can only be heard when the channel is idle (i.e no one is speaking). If I prevent media server from locking then there is no noise but of course the streams loose synchronization after a few minutes resulting in underflows on the server side. The noise is recorded in the attachment. Any guidance to resolve this issue will be greatly appreciated.
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Post by RitchRock »

Just a quick thought — I understand your custom PCB is very close, however is it possible to test with the Multichannel Audio Platform EVM board to see if the noise occurs?