nRF24 audio quality

[jimmykim]

I'm planning wireless conference system. 
This needs some condition as under
simultaneously use 5ch of wireless bi-directional connection through whole system.
Each wireless module use just one RF ch.

Each wireless channel use audio streaming(one direction) and small data transmission(bi-direction)

Is that possible with nRF24 ?

[ovrebekk]

Hi

Which nRF24 device are you targeting?

What quality audio do you need (sample frequency, bitrate) ?

The nRF24LE1/nRF24L01+ devices are not very well suited for audio, as the packet sizes are limited. I would recommend using the nRF52 series instead, where you are able to use larger packets, higher RF output power, and you have much more processing power available in the MCU for audio coding etc. 

The nRF52 family has also got a wider range of peripherals, such as PDM and I2S for audio transfer. 

Best regards
Torbjørn

[jimmykim]

Thanks 
If I use nRF52, how about audio latency ? is that OK for conference?
Also regarding data transmission, I want to set as 1:n .
That means controller can send control data to many mikes almost same time.

Finally my minimum technical goal is 32KHz sampling and 16 bit resolution. 
But if possible 48KHz, 24bit will be best to me.

[awneil]

jimmykim said:

32KHz sampling and 16 bit resolution

For a conference?!

That's better than CD quality!

I think that's going to be beyond the capabilities of BLE ... ?

[ovrebekk]

Hi

Audio latency is not the issue, unless you run very aggressive sound compression that requires a lot of buffering etc. 

The issue, whether you use the nRF24 or nRF52, is that you don't have a lot of throughput overhead if you want to send high quality audio. 

Uncompressed 32KHz, 16-bit, bidirectional sound requires a total data rate of 1024kbps. While this is technically possible in the 2Mbps proprietary mode in the nRF24 or nRF52 it won't leave you a lot of overhead for retransmissions, which means that packet loss will be very noticeable on the received audio since you don't have time to retransmit lost packets. 

Bidirectional 48KHz, 24-bit uncompressed is definitely not possible. The absolute maximum throughput in the 2Mbps mode is around 1700-1800kbps, and when pushing this much data you would have zero overhead for retransmissions, and you would have to expect significant packet loss in a noisy environment such as an office. 

Do you plan to have a single Nordic device in the central node communicating with all 5 devices, or multiple Nordic devices?

If the same device does everything you have to divide the total available bandwidth by 5. 

Best regards
Torbjørn