I am interested in SDR in general, and low latency CW / SDR on portable devices while back packing in particular. I used to be active in that field around years 2007-2008, while I developed the PocketDigi application for Pocket PC platform (the Pocket PC platform has been killed by Android some five years ago), and I was hacking digital modes on an Altoids tin size transceiver http://www.kufr.cz/~ok1iak/HAM/ATS3a-digital/index.php3
I built an Omnia basic transceiver, which is a reincarnation of the Peaberry SDR, for which I modified the firmware to support low latency CW transmit generated by the SDR board directly without any host support.
With the Omnia SDR transceiver, I was hoping to develop a lightweight back packing SDR CW setup. For CW, audio latency is important. With the help of the https://superpowered.com/latency application, I measured the following numbers on various Android devices, sorted by decreasing latency:
|Device||Android||Clock||Audio buffer size||Round trip latency|
|Onyx Boox C67ML (e-ink reader)||4.2.2||44100 Hz||1024 bytes||325 ms|
|Samsung SM-J320FN (smartphone)||5.1.1||44100 Hz||960 bytes||312 ms|
|Chuwi Hi8 Air (Win10/Android tablet)||5.1||48200 Hz||1152 bytes||269 ms|
|Nexus 7 (tablet)||4.2.2||44100 Hz||512 bytes||123 ms|
|Nexus 4 (smartphone)||5.1.1||4800 Hz||240 bytes||51 ms|
Interestingly, the Samsung phone shows a terrible round trip latency, while otherwise I am quite in love with the device. The old Nexus 4 phone shows the lowest latency, while still not close to the 20 ms round trip latency to be considered real time from a music performance point of view.