Thingy audio streaming

RE: Thingy audio streaming

Davide — Sat, 24 Mar 2018 15:31:54 GMT

Here we are, the source code of the ThingyTalkie project is available here: https://github.com/dgiovanelli/ThingyTalkie

To see what I changed/added just look at the last commit.

RE: Thingy audio streaming

Davide — Mon, 12 Mar 2018 13:16:33 GMT

Hello Norin,

sorry but you have to be patient for having the full code. Now it works but before sharing it I want to clean a bit the code. Within a week (but probably less) I will create a github project and I'll share the link in this conversation.

The links and code I used as example for developing my code are those posted by Nordic guys in this conversation.

Stay tuned!

RE: Thingy audio streaming

norin saiyed — Mon, 12 Mar 2018 10:53:21 GMT

Hello davide. Can you provide some useful links and reference code?? As i am also working on similar kind of an application.

RE: Thingy audio streaming

Davide — Thu, 08 Mar 2018 08:45:16 GMT

I reply myself because I did progress in the work and I have understood some thing that were actually not clear.

The Thingy can play 8bit PCM data at 8kHz. Although the mic outputs PDM data (1032kHz) the PDM interface of the nrf52834 includes a bandpass and decimation block which converts PDM@1032kHz to PCM 16bit@16.125kHz (data is downsampled by a factor of 64). Then to play the mic data into the speaker a further conversion from PCM 16kHz-16bit to PCM 8kHz-8bit is necessary.

I didn't realize the PDM interface includes the PDM-to-PCM decimation filter and that's was the main reason of all my doubts.

Now I manage to obtain some audio streamed between the two thingys, but it is still quite distorted.

RE: Thingy audio streaming

Davide — Thu, 08 Feb 2018 14:42:41 GMT

When it will work I'll share it. I manage to stream something but it is just noise, I have to dig deeper on how data is acquired/converted/compressed because for now I just have the speaker that play intermittent noise...

RE: Thingy audio streaming

redsun — Thu, 08 Feb 2018 14:26:55 GMT

Hello. Davide. Can you provide source code of your project, if it is not closed?

RE: Thingy audio streaming

Bjørn Kvaale — Thu, 18 Jan 2018 14:17:04 GMT

Thanks. There was a typo, yes. :) Good that you still understood what I was trying to write.

RE: Thingy audio streaming

Davide — Thu, 18 Jan 2018 11:32:10 GMT

Ok, now it is clear, the mic driver outputs PCM data and not PDM.

(I think there is a typo in your answer since it is quite difficult to output 8-bit pcm data with the mic, you probably intended to say "speaker").

RE: Thingy audio streaming

Bjørn Kvaale — Thu, 18 Jan 2018 09:56:28 GMT

Hi Davide, yes you are correct. Comparing the second link I sent you to the dvi_adpcm.c file in the Thingy_sdk_v2.1.0 shows that the two files are very similar (some small differences). Talked to an expert here at Nordic: the Thingy microphone uses ADPCM. The Thingy speaker uses 8-bit PCM.

Two small examples to clarify: when you stream music from a smartphone to the Thingy:52 using the Thingy app, the smartphone mic picks up 16-bit PCM. This 16-bit PCM is converted to 8-bit PCM in the Thingy app & then sent to the Thingy speaker, which outputs 8-bit PCM.

Conversely, the Thingy mic uses ADPCM, which is then sent over to the smartphone. The Thingy app then decodes the ADPCM into 16-bit PCM, which is sent to the smartphone speaker.

So to answer your question, the drv_mic.c file is encoded in ADPCM. Since no encoding & decoding is done inside the Thingy device, it might be helpful for you to check out the Android or iOS Thingy app and look for the decoder function from ADPCM to PCM (see the decodeADPCM() function in iOS for example).

RE: Thingy audio streaming

Davide — Wed, 17 Jan 2018 08:52:03 GMT

Sorry Bjørn, I have a further question. The second link you passed me seems to be the starting point for the audio driver of the thingy firmware right? If so I have a doubt, the code at that link provides the routines for converting from PCM to ADPCM and vice versa, instead inside the drv_mic.c it seems that the routine is applied to PDM data.

Now I'm a little bit confused, is the data in pdm_buf_t (drv_mic.c) encoded in PDM or PCM?

RE: Thingy audio streaming

Bjørn Kvaale — Wed, 17 Jan 2018 07:10:49 GMT

No worries. Good luck!

RE: Thingy audio streaming

Davide — Tue, 16 Jan 2018 15:43:58 GMT

Super! Thank you!

RE: Thingy audio streaming

Bjørn Kvaale — Tue, 16 Jan 2018 14:45:35 GMT

Talked to a few experts here at Nordic: you should use an ADPCM decoder, yes. You can take a look at this decoder written for Node.js. Otherwise, this decoder written in C might also be helpful.