Hi all, audiophiles included (like myself),
Just wanted to remind that any HF equipment doesn't deserve to be called
SSB transceiver if it has no equalization of the transmitted signal. It
is extremely important in SSB DX work when you want to get through the
QRM and other noise. As Bob let us understand, SSB, AM and FM DO NEED
shaping. We do not need flat frequency response for the best
intelligibility with the legally or technically limited powers and
bandwidths. In addition to the frequency shaping we need amplitude
compression or even clipping. Read this article from 1970's, it is still
true: http://kotisivu.dnainternet.net/ahti/sdr-1000/filtclip.pdf . Now
with the DSP tools we can make everything in a more elegant and
efficient way.
Merry Christmas and Happy New Year with the wonderful presents from
FlexRadio,
73, Ahti OH2RZ
- Original Message -
From: Robert McGwier [EMAIL PROTECTED]
To: Tim Ellison [EMAIL PROTECTED]
Cc: FlexRadio@flex-radio.biz
Sent: Friday, December 23, 2005 8:29 PM
Subject: Re: [Flexradio] Change to floats in Preview 9, speed up, and EQ
Gerald, Frank, Eric, and I have come to an agreement on what the new
EQ
will look like. It will not be like a ISO centered RANE lookalike(
but
not function-alike !) but will provide the necessary shaping so that
you do not get this very flat response that sounds so different on TX
from that which people are accustomed to (they are accustomed to at
least a bit of preemphasis and some other shaping). The new EQ will
be
10 bands or less and not work above 6 KHz. We will concentrate on
those
areas where SSB, AM, and FM needs the shaping. It will be implemented
using 512 sample buffers to limit latency to 11 ms. This was NOT that
different from the delay through the low frequency filters in the IIR
version.
Expect this out in preview 10.
Your results are consistent with mine. We are taking cache hits 1/2
as
often on average and the total memory bandwidth demands are down under
50% from before. Slow off chip (not cache) memory was a big limiting
factor before. The use of floats in the optimized FFTW routines more
than make up for the slightly loss of speed when the floating point
unit
is used to do floats/doubles. Many functions automatically promote to
doubles so this can be a net loss. In this case, the overwhelming
increase in speed in FFTW3 more than makes up for the occasional
sin/cos
promotion to double and then conversion back to float. Also, we just
left the oscillators running as doubles so the phase wrap glitch
occurs
once a week!
On my wife's sempron, with almost no cache, the lowered memory
bandwidth
demand dropped it from 65% to 25%.
Thanks and again, our apologies for not testing the EQ after the
change.
Bob
N4HY