[RTTY] MMTTY curious problem

[Ekki Plicht]

During the SCC contest I experienced some new problems with MMTTY...

Somewhen in the early morning I couldn't print anything, although the signals 
sounded OK, the XY-display of MMTTY showed a nice signal as well. I noticed 
that the spectrum display above the waterfall of MMTTY was somewhat elevated 
and a fast and small oscillation overlaid to the overall signal. 

Looked to me like that MMTTY  filter began oscillating by itself. I know that 
filters (real) can oscillate, and I suppose that simulated filters can show 
the same behaviour... but never seen this before in MMTTY.

The only remedy was to move the Mark frequency off from where it was, then set 
it back again to the original value (2125 Hz). Or leave MMTTY (RckRtty) and 
restart.

It happened both with IIR and FIR filters, not with with PLL. I seems to me as 
if it happened more often on a quiet band, like 20m early in the morning. 
After my break, where I turned off the PC, it was working fine for the rest 
of the contest. Maybe a temperature problem from the soundcard?

Does anybody know where this comes from?

73,
Ekki, DF4OR