Thingy Audio After ADPCM decode, what is the frequency?

[jublin]

I have a windows side application and an Android App, both of which are set to capture data from the Thingy Sound Service. 

On the windows application, the data after being written to a file looks like 16kHz Audio. 

On the Android application, it looks like 8kHz, when looking at the number of samples written.

Which one is supposed to be correct? I know the Thingy sends of BLE in 8-bit/8khz encoded, but the raw data is 16khz/16bit. The waveforms both look similar, it's just the amount of data in each file.

[Jiajun]

The thingy firmware supports only 8-bit/8khz encoded. If the raw data is 16khz/16bit, the app will truncate it to 8bits and send it to the Thingy device. 

[jublin]

I'm asking the opposite. When the Thingy sends to the app, and the app decodes through ADPCMDecoder, what frequency should the data be? I'm seeing stuff around 8khz when graphing the audio data, but on the windows app side, the data saved appears to be 16khz.

[Jiajun]

When you using the microphone on Thingy, the data stream will be 16bit*16kHz/4 = 64kbit/s (ADPCM compressed 4 times). After ADPCM decode (uncompressed) you get 16bit*16kHz=256kbit/s. When sending to Thingy speaker service data should be 8-bit*8khz = 64kbit/s (Uncompressed)