Dear Ti,
I've some unwanted 1Khz tone on the output of the PCM2900C USB codec. The codec is used in a mixer that i designed and users complain about a 1Khz tone. I did some research and some measurements and i want to share these results and want to know if this is a normal phenomenon.
First of all the 1Khz tone is only heard when the recording channel is somehow selected or addressed by a software program. The way i tested this is by selecting the recording devices tab of the sound devices window.
Reference measurement. Output of the mixer connected to my AP sys2522 with the audio devices windows selected on playback devices:
As can be seen in the measurement is that the 1Khz is present at -70dB, if four chanels are full open than the level reaches -55dB ;(
Full bandwidth 48KHz 16Bit stereo out and 48KHz 16Bit Stereo in (recording)
Altering the recording channel settings reduces the signal a small bit. First i switched back to mono recording:
48KHz 16 Bit out and 48KHz 16 bit mono in (Recording)
Altered the playback channel settings back to 32KHz sampling rate:
32KHz 16 Bit out and 48KHz mono in (Recording)
The lowest setting gives the lowest signal
32Khz 16Bit out and 11KHz 16bit in (recording)
As long as any application doesn't address the recording of the codec there is not a problem. but most application do and also if the customer is recording something the 1Khz tone is very unwanted.
I also noted the http://www.ti.com/lit/er/slaz036a/slaz036a.pdf SLAZ036A Errata noting somethin about a 1Khz tone when the devices is used in some of its modes. The errata only describes the problem of unwanted 1Khz tone in its tranfered data, so not in the output of the codec.
I also compared my findings with a Behringer UCA202 that is equiped with a PCM2902 and found the same tone.
Is this problem know at TI and is there a fix ? please help
Kind regards Jaac
