Did some benchmarking between Fldigi and the Java modems in THOR22 and THOR11. I was running both Fldigi and the Java client 2 on the same machine so the data they were receiving from the sound card was the same.
Thor 22 decoded down to -12 dB ( one or two errors per 100 characters). Same results on both with a very very slight advantage to Fldigi due to better re-sampling I believe, but really marginal and visible only at -13dB in white noise.
Thor 11 decoded down to -15dB with the same error rate as above. Same difference between Fldigi and Java: sometimes the Java modem will decode blocks properly at -16dB and sometimes Fldigi will, so it is really the same from a practical point of view.
RSID detection comparing stock Fldigi (original hamming distance = 1 max) and Java modem with hamming distance = 5 max:
@ -15dB white noise: Fldigi 1 out of 10 transmissions, Java modem 7 out of 10.
@ -14dB white noise: Fldigi 4 out of 10 transmissions, Java modem 9 out of 10.
@ -13dB white noise: Fldigi 9 out of 10 transmissions, Java modem 8 out of 10.
@ -12dB white noise: Fldigi 8 out of 10 transmissions, Java modem 9 out of 10.
@ -11dB white noise: Fldigi 9 out of 10 transmissions, Java modem 9 out of 10.
No false positives in either Java or Fldigi (expected in the later one). So with the modifications to the Hamming Distance we are at or better detection level than stock Fldigi.
Reviewing the weekend log of the server with a modified Fldigi with hamming distance of 5, I had 5 false positives. So I decided to try with a value of 4 maximum. That is running now.
Testing in the same context as above between Fldigi (HD = 4 max) vs the Java modem (HD = 5 max) I get the following results:
@ -16dB in white noise Fldigi gets 8 out of 10 and Java modem 7 out of 10. The better re-sampling is visible there.
So in summary for RSID: Both Fldigi and Java modems benefit from the relaxed matching criteria without side-effects so there is real benefit to change both to a max level of 4 (Fldigi) and 5 (Java modems due to smaller set of RSIDs possible). Exact values to be validated by field trials.