My RD-5R gives about 0.4% BER when talking to my MMDVM hotspot, but my GD-77 with the same configuration gives nearly 1.0% BER. Audio quality is still good, but of course it's worthwhile to tune things to minimum error rates regardless.
Some notes on tuning the TX level on the radio:
N6AMD, How to tune your MMDVM repeater with an SDR for low BER. Focuses on getting your audio levels correct; "If the raw audio is either too quiet or too loud, subscriber radios will not decode the digital signal properly." Uses
pistar-mmdvmcaland an SDR to calibrate audio levels (TXlevel).
F5UII, Install MMDVMHost on Raspberry Pi and tuning MMDVM for DMR digital mode . N6AMD's article is derived from this one, which uses both SDR and oscilloscopes for tuning. "The goal is simply that the audio levels are not too strong and do not saturate the analog input of the arduino".
Some notes on tuning the RX offset on the hotspot
- Ailunce, How to set RX TX offset. "Also every DMR radios may get a different BER when using the same hotspot. If you can't find a good balance for the BER between the different modes, it may be better to use different hotspots for each different mode."
Thanks to Christopher M0YNG on Feditalk to help me with some tuning ideas.