Delay in Linrad-03.34
Leif Asbrink
When 03.34 is used with the second FFT, the processing blocks
are not delivered one by one from the second FFT, but in groups
of two or sometimes even three transforms. Th accomodate for
this it is necessary to set a large output delay margin. Otherwise
there would be drop-outs in the audio each time a new station is
clicked.
With 3Hz Hz bandwidth the extra delay is in the order of 800 ms.
To accomodate for that one has to set an output delay margin
of 1000 or so.
To fix the error, edit line 379 in fft2.c:
if( ((timf2_pn2-local_timf2_px+timf2_totbytes)&timf2_mask) >=
Change it to:
if( ((timf2_pn2-timf2_px+timf2_totbytes)&timf2_mask) >=
This error happens on computers with 2 or more CPU cores.
After this correction my Compaq 6510b needs an output delay
of 150 ms when I run at 125 kHz sampling rate under Linux
with float arithmetics and no MMX instructions. If other
programs are running in parallel it could be necessary
to set a somewhat larger margin.
73
Leif / SM5BSZ