Bluetooth LE Audio - Question

[davidzweig]

Hello,

I have a question about hardware for Bluetooth LE Audio.

I see Nordic is working on a dev kit:

https://blog.nordicsemi.com/getconnected/le-audio-unveiled-as-the-next-generation-of-bluetooth-audio-and-nordic-will-be-a-key-player

I found a bit more information (https://www.eenewsembedded.com/news/evaluation-platform-expected-le-audio-specifications):

"The new LE Audio solution contains a hardware reference design built around Nordic's nRF52832 Bluetooth LE SoC, Cirrus Logic's CS47L35 smart codec with integrated low power Audio DSP, Packetcraft's Bluetooth LE host stack and link layer supporting LE Audio, and an LE Audio SDK.

The LE Audio Evaluation Platform can operate both source and sink modes. Both a source and a sink are needed to create an LE Audio link. The platform also uses Cirrus Logic's SoundClear for uplink noise reduction and echo cancellation, playback enhancement, voice control, and hearing augmentation."

Datasheet for the Cirrus Logic chip: https://statics.cirrus.com/pubs/proDatasheet/CS47L35_F3.pdf

My question:

If I were to try to create a basic LE Audio speakerphone, that pairs with a smartphone, is the Cirrus Logic chip required? I'm guessing the nrf52832 has sufficient processing power and ram to decode/encode speech-quality LC3. It also has microphone inputs, and I2S or PWM for audio output. Echo cancellation might be difficult to do on the nrf52, but, can this be handled somewhere in the Android/iOS stack, on the smartphone (with the speakerphone still presenting itself to the smartphone as a regular 'audio device')? Perhaps also noise reduction? I hope my question is clear.

Best Regards,

David

[bjorn-spockeli]

Hi David,

If I were to try to create a basic LE Audio speakerphone, that pairs with a smartphone, is the Cirrus Logic chip required?

I'm guessing the nrf52832 has sufficient processing power and ram to decode/encode speech-quality LC3.

That will depend on the LC3 implementation I would say.  In our Smart Remote 3 reference design we support  the following codecs:

• ADPCM,
• BroadVoice32 (BV32FP)
• Opus (SILK and CELT)
• SBC (including mSBC)

where I think OPUS is the most comparable to LC3. We do support active noise reduction (ANR) when using two PDM microphones, see https://www.vocal.com/noise-reduction/adaptive-noise-reduction/. They also have a Echo cancellation library, see https://www.vocal.com/echo-cancellation/, I beleive we tested this with the Smart Remote 3 design, but did not add it as the non-optimal location of the microphones resulted in no-more than average results. Also we only keep the microphones on for short amounts of time in the SR3 to reduce the current consumption, while it is optimal that they are on 100% of the time for echo cancellation. If doing echo cancellation on top/ in addition to ANR and audio decoding is feasible with regards to processing power, I do not know. 

It also has microphone inputs, and I2S or PWM for audio output. Echo cancellation might be difficult to do on the nrf52, but, can this be handled somewhere in the Android/iOS stack, on the smartphone (with the speakerphone still presenting itself to the smartphone as a regular 'audio device')?

If you do not need the audio-grade DAC, the amplifier and the 3 DSPs for uplink noise reduction and echo cancellation, playback enhancement, voice control, and hearing augmentation, and are satisfied with the I2S and PWM periperals on the nRF52, then I guess you can remove the CS47L35. However, I do not know how the current consumption numbers will be when doing audio decoding, ANR and Echo cancellation on the nRF52 opposed to offloading this do a dedicated chip like the CS47L35. 

Best regards

Bjørn

[davidzweig]

Dear Bjørn,

Thank you for the informative response. I see the CS47L35 also has an integrated 2.5W amplifier, this is nice. But, it will add about $5 USD to the BOM it seems (https://lcsc.com/search?q=CS47L35). For our application it's probably too expensive.

Best Regards,

David

[bjorn-spockeli]

Happy to help. Let me know if you have any other questions. 

Best regards

Bjørn