Stereo Tool

So, where are things with SSBSC MPX? Any thoughts about when this might make it into the code base?

I was thinking that you didn't want to use RDS the highest frequency you'd have to produce would be 38 KHz L-R center frequency. That would mean that a 96 Ksps audio card would work. The Nyquist rate being 76 Ksps.

Bill

No update yet, but I read an article on Radio World that Frank Foti posted on Facebook, and I'm wondering if anyone could comment on my comment?

http://radioworld.com/article/fm-ssbsc- ... ons/214190

And this is what I'm thinking:

The article states that the Omnia 9 and 11 use DSB for very low (below
150 Hz) frequencies, SSB for the rest. I have not done any calculations
and I have no real experience (yet) with SSB, but this seems
counter-intuitive.

Basically, multipath distortion gets worse when the frequencies get
higher, but also when the amplitude of these frequencies gets higher, right?

So, if you have a 15 kHz tone:
DSB gives you 2 spikes, at 38-15=23 kHz and 38+15=53 kHz.
SSB gives you 1 spike, at 23 kHz, with twice the power.
The difference between 23 and 53 kHz is huge, so it makes sense that SSB
wins.

But if you take a 2 kHz tone, the situation might be very different.
DSB again gives you 2 spikes, at 36 and 40 kHz.
SSB gives 1 spike at 36 kHz, which is twice as loud.
In this case, 36 and 40 kHz are pretty close together, and a twice as
loud 36 kHz tone might very well be worse than having two different
tones. Looking at the combined waveform (36 kHz sinusoid + 40 kHz
sinusoid), the stereo signal peak level will be the same for SSB as for
DSB, but for SSB it will be reached far more often. We're not interested
in peak level though, but in motion (slope). The maximum slope will be
slightly bigger for DSB, but it will change continuously. For SSB the
same slope values will repeat constantly, giving a constant sequence of
disturbances. I am not sure what that means though, especially since you
need to take into account how receivers work - but my guess is that
continuous disturbances will sound worse.

If this is true, it should be possible to determine an 'optimal DSB/SSB
slope' which might differ from what is currently being used in these
tests. Whether this is true depends on whether a single loud frequency
is worse than 2 softer frequencies, and since that also depends on how
receivers work, I guess this would require more tests.

It sounds to me, from the explanation, like Frank started with a pure SSBSC 38KHz LSB subcarrier but found that some receivers were upset and started blending to mono way before they had a reason to resulting in loss of separation. Adding the low frequency part of the USB made the receivers happy. He probably limited the frequency to just what was needed and no more since part of his thesis is that that would create more mix pairs and the reduction of perceived noise because of the frequency inverted LSB would become more and and more of an issue as the USB was extended up in frequency.

Bill Putney - KPTZ Port Townsend, WA

I'd like to test SSB MPX because I think i't better than classic system, lower bandwidh etc..
But I can't find any software to generate on PC I'm waitanig for this option in ST

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Urban Junglist

I'm not really sure how big the improvement is (also talked with Leif about this, and he also has doubts). Anyway, I need a composite clipper before I can implement this. And that's on the roadmap - but after at least the GUI and a new multiband compressor.

I know that is not full compatible with all fm tuners, some problems may be, it is too late for this system but lower bandwidth always is better then higher...
I will work on hardware dsp encoder for education experiments, ssbsc also I want to try, now is to hard for me I thin ST will have this option faster then me..

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Urban Junglist