Hi out there – I found the problem with the buzzing noise, there was a short on the VDD_Analog and RCAP Pins on the LQFP Package of the VS1063. Now the thing sounds quite decent. It still needs some fine tuning. Help for this is on the Way, I will meet an Audio Engineer probably next week.
Meanwhile I put together the device to see if there are any mechanical problems – but Verficiation in 3D (with SketchUp) paid off and no problems when assembling the device – well there are some minor issues with the housing but those are basically translation errors to the punching machine.
And to see how the VS1063 performs with various bitrate settings I added support for statistics to the STM8 Firmware. With the help of the STM Studio Tool which allows non-intrusive debugging it is now possible to monitor the bitrate and buffer status in realtime. The bitrate shows the average bitrate in the last 1/4 second – whereas the buffer status shows more or less random the current bufferstatus – because the update rate via the STM-Link is limited.
Run 1: CBR Mode with 128000 bps
This shows that we have some Peaks with around 170000 bps and average around 130000bps.
Run 2: Quality Mode with q=10
Bitrate varies between 250000 and 400000 bps
Run 3: Quality Mode with q=1