nRFready audio compression/transmission resource profiling

Question

Hi there, 
 
 I have an nRFready Smart Remote 3 in front of me to evaluate for development of an upcoming product. I've had a look around the forums and documentation, but haven't found too much detail as yet. Is there any information available on resource usage on the nRF52 when using the audio streaming features? I imagine there's a bunch of DSP and compression that happens before transmission, and then the BLE payload is probably significant. 
 Is there any benchmarking for CPU/battery/etc when implementing the audio streaming sample project? If not can you point me to some info on a good way to do this benchmarking? 
 Thanks, 
 Tom

Filip Kubicz · Accepted Answer

It is best to benchmark in your specific use case. I can give you some rough estimates in the default firmware configuration: - ADPCM encoder CPU usage is ~3% - SBC encoder in mSBC mode ~ 5% CPU - Opus CELT VBR with 20ms audio frame: - complexity 0: ~28% CPU - complexity 4: ~40% CPU - complexity 10 ~75% CPU - Opus SILK VBR with 20ms audio frame: - complexity 0 ~49% CPU - complexity 4 ~75% CPU Opus has a higher CPU consumption than other codecs, however it gives you great sound quality with high compression ratio - which means you need less bandwidth on Bluetooth Low Energy and thus the overall power usage (CPU + radio) is lower. Opus CELT VBR is a good choice for a very power efficient application. If you want to minimize CPU consumption for Opus, it's best to use GCC with LTO and O2 optimization level. Also, to use less CPU do not use --specs=nano.specs.

Filip Kubicz · Answer

Hi Tom, First of all, thank you for interest in Smart Remote. In Smart Remote 3 v1.1 , after each finished audio transmission over BLE you will see a report: - min/average/max CPU used by audio module - min/average/max CPU used by codec - min/average/max audio bitrate - similar benchmark for Acoustic Noise Reduction (ANR) if it is enabled The benchmarking is enabled by default, so you can see it if you flash precompiled firmware. You can see how the benchmarking is done in Source/Debug/m_audio_gauges.c . It is also easy to adapt the code to measure CPU usage of your custom audio algorithm. For reference, please have a look at m_audio_process() function in Source/Modules/m_audio.c . EDIT: you can display total CPU load measured at 1 second interval if you enable CONFIG_PWR_MGMT_CPU_USAGE_MONITOR_ENABLED . Good news for you is that in the new Smart Remote release, which is coming in a couple of weeks, firmware is going to be even more helpful in this matter. It has command-line interface with commands for checking audio subsystem settings and changing them in runtime. The benchmark framework counts lost frames (in case BLE bandwidth is not enough for audio) and lost buffers from microphone (in case the CPU is too busy to process audio). The framework also informs you what's the current and maximal usage of queues with audio data, so you can tune memory settings. Testing of audio algorithms should be easier, too. New release comes with audio instrumentation framework which lets you capture or inject sound at any stage of DSP processing in Smart Remote. I hope this helps. Kind regards, Filip

nRFready audio compression/transmission resource profiling

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