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CC2564C: Unassisted mode and HSP encoding

Harold Ducept
Prodigy 60 points
Part Number: CC2564C

Hi!

We want to use the CC2564C to develop a product that will have to manage an HSP connection in parallel with a BLE connection.

1st question: According to the datasheet, it means that we cannot use the assisted mode, therefore, having to manage audio encoding externally. But I think I've seen on TI's forum that if we are in Narrow Band Speech, we should still be able to have the encoding done by the BT module. Which one is correct? How to enable NBS? Haven't found any information about that. We use BlueKitchen stack.

2nd question: In case we cannot go for NBS, we want to get the audio encoded by the MCU. This one would send audio data over I2S. From what we understood, we should implement a CVSD encoding algorithm. According to wikipedia, this algorithm seems to have a "1 sample per bit" output. Does that mean that to get a 16kHz signal, we need to provide 16*8=128Khz sampled signal? Is that correct? That looks like a lot to us!

Thanks,

Harold

  • 0
    TI__Genius 9585 points

    Hi Harold,

    I am looking into this, ill keep you updated when I have a proper answer.

    Kind Regards,

    Rogelio

  • 0
    Prodigy 60 points

    I've finally managed to answer myself to my questions. For the next one having the same problem:

    • By default NBS is enabled. WBS is enabled by defining ENABLE_HFP_WIDE_BAND_SPEECH
    • When NBS is enabled, audio is indeed encoded by the CC2564C
    • When in NBS, audio can be transmitted either over I2S or HCI (using ENABLE_SCO_STEREO_PLAYBACK or ENABLE_SCO_OVER_PCM)
    • When using WBS (meaning audio being encoded by the MCU) audio has to be transmitted over HCI
    • My 2nd question doesn't make any sense. The purpose of encoding is to reduce the amount of data. Encoded data cannot be transmitted over I2S and if I want a 16kHz sampled signal, I will get a 2kHz CVSD signal.

    Hope I didn't make any mistakes in my details here!

    Harold