We are having a funny delay in the microphone input when we try to make a recording. All recordings at 8 and 16bits per sample and from 8kHz to 48kHz sampling, mono or stereo show the same response. I am attaching recordings of a 1kHz tone. (sent to Gandhar Dighe) The attached 30second 1khz wav file is played out of a PC using media player into the mic on the cozumel device. When playing out of the normal PC speakers the wave file shows no significant distortion or phase change events.
What is seen and heard when this wave file or others are recorded on Cozumel are:
1) every multiple of 2 seconds from the start of recording a phase change of the continuous tone is recorded. This sounds as a pip every 2 seconds. see Cozumel Mic Record 2s phase.jpg. You will be able to hear it in the 8b_16k_m_1k.wav file too.
2) When the start recording event is initiated by pressing the record button on say Windows Notes app or any other recording app on Cozumel, the recording has a start up delay of around 1.5s before it stabilises to optimum levels. This can be seen in the attached file Cozumel Mic Recording.jpg. The file shows recordings of 1kHz tones at 8bit and 16 bit mono at 16khz and at 16bit 48khz stereo. However the artifacts are the same irrespective of any setting of sampling values.
3) In the stereo recording left and right channels show different gain settings.
Once the recording stabilises after 1.5s or thereabouts, the distortion is within the experimental setup limits. See Coz mic dist 8b 16k 1khz - freq spectrum of a 1kHz tone recorded at 8bits 16khz sampling rate. This data is taken when the mic recording has stabilised.
The file Cozumel Mic Record start.jpg shows a close up of the start recording event sequence. Also attached is a schematic path overview for the mic to codec path in Cozumel Mic.jpg - schematic of the mic connection from the 65950 to the PDM digital mic on the keyboard.