Stereo Tool

Hi Hans,

It would be great if you insert some sliders in the Stereo/RDS part.
a level control for:
RDS Signal
Pilot Signal

and Phase of these signals.

Grtz Gijs (uut marienheem)

Hi Gijs,

Volume level sliders for those two were already on my todo list (I forgot to add them, actually I wanted to put them in version 3.20... Well, I'll probably add them to 3.21 then).

Question: Why do you want to change the Phase of the two signals? Is that to fix offsets that are introduced by the sound card, or for other reasons? (The answer to this has implications on how it should be implemented).

the phase thing:

The most soundcards are not phase linear till 60khz.
Some adjustments could be made. As I do right now with airomate.

grtz Gijs

Ok, here's the thing:

The STEREO signal ranges from 23 to 53 kHz. I suppose when adding a phase shift I should shift 23 kHz differently from 53 kHz. AFAIK (please correct me if I'm wrong) Airomate just changes the phase of the carrier frequency, which means that the other frequencies shift also. But they probably won't switch the right amount.

For RDS the problem is much smaller, because it only ranges from 55.6 to 60.4 kHz.

Do you have any information about how the sound cards change the phase of the sound? If you do, I might be able to correct for it much more precisely than when I just change the carrier frequencies phase. The latter would work very good for bass frequencies, but less good for higher frequencies.

Note: I see 3 possibilities:
1. Phase shift is directly proportional to the phase. So PhaseOffset(FreqX) = constant * FreqX.
2. Phase shift is directly proportional to the phase, plus an offset. So PhaseOffset(FreqX) = constant * FreqX + offset.
3. Phase shift is not directly proportional. There's no (simple) function to calculate it.

(1) would mean that I have to add 1 phase shift slider (which would work for both Stereo and RDS signal)
(2) would mean adding 2 sliders: One for the phase shift, one for the offset (which would still work for BOTH Stereo and RDS).
(3) would be very problematic...

Ideally Stereo Tool would measure the offset in the output, but I suppose that the input will cause an offset as well. So I cannot accurately measure the introduced offset.

Hi Hans,

Well actually I'm not so deep into this but what I think the phase sliders are for the carriers so they won't interfere with each other. The third harmonic of the 19khz is 57khz.

I have a cheap as broadcast analyser (http://www.pira.cz) and this is measuring the phase difference between the carriers.
With airomate it depends on the card if the phase is correct or not. The most ENVY24HT chips are reasonably good.

But I'm not sure if you want to change the complete phase or not.

grtz Gijs

Ok, so you can measure them! Can you give me the phase offsets that are reported? That would probably help me to determine the best way of fixing it.

Pilot tone and RDS Volume have been added to the latest 3.20 beta version. For the phase correction I'm waiting for your Pira results...

If the differences are small (say less than 30 degrees for the RDS signal), I'll use a very simple approach. If higher numbers also occur, I might need to do something more complex.