NRF52810 antenna throughput while sampling pcm from pdm interface

[chrismoi]

Hello Devzone,

I've been using nRF52810, SoftDevice 112 (5.1.1), for a Mic recording application. What I'm trying to do is sample PDM MEMS mic data through PDM interface and send simultaneously the PCM samples over bluetooth. With a buffer size of 500Bytes, pdm interval from buffer to buffer is ~12ms, which seems enough for a 500Byte bluetooth transmission since 1Mbps PHY means that theoretically I can send 500Bytes->4Kbits in 4ms

My Bluetooth settings were: MIN_CONN_INTERVAL : 8ms, MAX_CONN_INTERVAL : 11ms, aggreed MTU with iPhone 6s was 185 Bytes, Gap data length 251, Gap event length tried different values (3,6,9,12,15,20,30) all with the same results. The maximum resulted throughput was 50% of the PCM samples.

First of all and before I lay out some code, I would like to understand if what I'm trying to do is even possible with nRF52810.

[Kenneth]

You can find various throughput numbers here for the S112:
https://infocenter.nordicsemi.com/topic/sds_s112/SDS/s1xx/ble_data_throughput/ble_data_throughput.html

Though I recommend to check out the S113 (or any other softdevice that support Data Length extension), since that will have a major impact on the throughput (see table 2):
https://infocenter.nordicsemi.com/topic/sds_s113/SDS/s1xx/ble_data_throughput/ble_data_throughput.html 

Also, I think the limitation here may not be the nRF52810, but the resources you can get from the iPhone. Check out chapter 25.6 Connection Parameters:
https://developer.apple.com/accessories/Accessory-Design-Guidelines.pdf

[chrismoi]

OK thanks for the feedback,

so in order to send voice data to any mobile (at least bl4.2 and further), would a practical solution be that I keep first 8-bits from every 16-bit sample, halving the bitrate? Would this loss be negligible for a human speech recognition application?