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 Post subject: Re: Stereo Tool 9.00
PostPosted: Fri Jul 20, 2018 12:58 pm 
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At the level where I can no longer decode RDS via RDSSpy from the PIRA using the microMPX output (same card type), can switch across to the MPX output into the same TX and reduce power by another 15-20% before I loose RDS from the MPX derived from ST directly.
O. That's actually very surprising and unexpected - unless the fact that you lowpass at a very low frequency is helping the RDS. The actual audio signal does NOT overlap with the RDS.

Do you know if the same difference is also there if you move the Stereo Tool lowpass filter up to 16.4 kHz (the maximum)? Because that's also the default setting in the Omnia.9sg etc - so if this affects RDS reception we might need to change that value everywhere. It also could be that RdsSpy is affected by this but actual receivers are not - more testing needed I guess.

If this is indeed affecting RDS then we need to fix it (and we can - until now we didn't think it made any difference).


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 Post subject: Re: Stereo Tool 9.00
PostPosted: Fri Jul 20, 2018 2:27 pm 
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Location: Bulgaria
Quote:
Quote:
Stereo Tool 9.02 BETA015
Windows 64 Bit Standalone B015 + microMPX B016

ST902-B015_microMPX-B016.JPG

Would be possible (or worthwhile) to add a command line to microMPX to allow for a pilot and/or RDS guard (filter) to protect either of them from transients/audio spikes?

The top is ST output into a low power test TX, the bottom is me decoding the same signal via MPXTool.
At the level where I can no longer decode RDS via RDSSpy from the PIRA using the microMPX output (same card type), can switch across to the MPX output into the same TX and reduce power by another 15-20% before I loose RDS from the MPX derived from ST directly.
I realise that some of this stems from the the nature of the codec (per previous post) but thought I'd throw the idea up for review.

Cosmetic display bug: The FM Lowpass frequency value is being shown on the main screen for both the FM and Bandpass Lowpass frequency values.

Rossco
Excuse me,
What is your low pass frequency ? Did i see it`s low than 15 kHz ? Or It`s just an "optical lie"?


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 Post subject: Re: Stereo Tool 9.00
PostPosted: Fri Jul 20, 2018 2:40 pm 

Joined: Sat Nov 10, 2012 2:16 am
Posts: 91
Location: Australia
Quote:
Excuse me,
What is your low pass frequency ? Did i see it`s low than 15 kHz ? Or It`s just an "optical lie"?
For that particular test - 13500.
I have been backing it off from 16400 (max) to see if there is any improvement to separate the audio away from the pilot and RDS without compromising audio quality.

Rossco


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 Post subject: Re: Stereo Tool 9.00
PostPosted: Fri Jul 20, 2018 2:55 pm 

Joined: Sat Nov 10, 2012 2:16 am
Posts: 91
Location: Australia
Quote:
Do you know if the same difference is also there if you move the Stereo Tool lowpass filter up to 16.4 kHz (the maximum)? Because that's also the default setting in the Omnia.9sg etc - so if this affects RDS reception we might need to change that value everywhere. It also could be that RdsSpy is affected by this but actual receivers are not - more testing needed I guess.
Here are a couple of non RDS outputs for comparison (will see if I can run RDS test again here also at 16400 and post if you like).
Ran non RDS test to show the composite signal spiking into the RDS space versus how it looks direct from ST.
Realise there is a trade-off for the IP carriage and codec - just wondered from the original post whether something like a notch filter could be used to guard the pilot or rds...

ST MPX 16400 LP no RDS.
Attachment:
ST902-B015_16400.JPG
ST902-B015_16400.JPG [ 37.85 KiB | Viewed 2682 times ]
microMPX 16400 LP no RDS
Attachment:
microMPX-B016_16400.JPG
microMPX-B016_16400.JPG [ 38.01 KiB | Viewed 2682 times ]
MPXTool sees more Pilot modulation at 16400 compared to running LP at say 14000/14500/15000.
Best results (no modulation over a 10min sample) was 14000 or less.

Rossco


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 Post subject: Re: Stereo Tool 9.00
PostPosted: Fri Jul 20, 2018 2:58 pm 
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Joined: Wed Nov 19, 2008 7:44 pm
Posts: 1127
Location: Bulgaria
Quote:
Quote:
Excuse me,
What is your low pass frequency ? Did i see it`s low than 15 kHz ? Or It`s just an "optical lie"?
For that particular test - 13500.
I have been backing it off from 16400 (max) to see if there is any improvement to separate the audio away from the pilot and RDS without compromising audio quality.

Rossco
So, if you make it 15000 (or even as Hans said 16400), Those "side effects" from coding in uMPX, will go "into" the RDS


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 Post subject: Re: Stereo Tool 9.00
PostPosted: Fri Jul 20, 2018 3:14 pm 
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Joined: Mon Mar 17, 2008 1:40 am
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Quote:
Quote:
Do you know if the same difference is also there if you move the Stereo Tool lowpass filter up to 16.4 kHz (the maximum)? Because that's also the default setting in the Omnia.9sg etc - so if this affects RDS reception we might need to change that value everywhere. It also could be that RdsSpy is affected by this but actual receivers are not - more testing needed I guess.
Here are a couple of non RDS outputs for comparison (will see if I can run RDS test again here also at 16400 and post if you like).
Ran non RDS test to show the composite signal spiking into the RDS space versus how it looks direct from ST.
Realise there is a trade-off for the IP carriage and codec - just wondered from the original post whether something like a notch filter could be used to guard the pilot or rds...

ST MPX 16400 LP no RDS.

ST902-B015_16400.JPG

microMPX 16400 LP no RDS

microMPX-B016_16400.JPG

MPXTool sees more Pilot modulation at 16400 compared to running LP at say 14000/14500/15000.
Best results (no modulation over a 10min sample) was 14000 or less.

Rossco
Ok. We'll look into this when Mathijs gets back from his holiday. The signal shouldn't spread out beyond the 16400 whatever you send to it - something isn't doing exactly what it should right now. The levels are pretty low though so I wouldn't expect them to actually influence anything (having audio close to the RDS area might though).

There have been processors on the market that had a signal that was way louder than what you're seeing here that went on even beyond 70 kHz.....


Edit: In the display in MicroMPX itself - which goes down to -90 dB - I don't see this at all.
Edit #2: Occasionally a small spike on the right of the L+R area. It seems to peak at around -85 dB. While I agree there should be nothing at all there (and we will look into it - it can't be that hard to fully get rid of it) I can't imagine that it affects anything in the real world. Many popular processors that are used everywhere have less than 70 dB pilot protection - and that's constantly, not sometimes an occasional spike. Both measured with Stereo Tool.


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 Post subject: Re: Stereo Tool 9.00
PostPosted: Fri Jul 20, 2018 4:13 pm 
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I don`t know why, but Encoder "sees" at "Main input" only the virtual cable here and shows "invalid device" when i select "whatever" option.
In the list there is no "the real sound cards"


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 Post subject: Re: Stereo Tool 9.00
PostPosted: Fri Jul 20, 2018 4:15 pm 
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Quote:
I don`t know why, but Encoder "sees" at "Main input" only the virtual cable here and shows "invalid device" when i select "whatever" option.
In the list there is no "the real sound cards"
It only shows 192 kHz capable sound cards. Could that be it? That's 192 kHz for input.


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 Post subject: Re: Stereo Tool 9.00
PostPosted: Fri Jul 20, 2018 4:30 pm 
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@rosco:

Aaaaah. Ok. So, the issue you were having has NOTHING to do with the signal quality. In MicroMPX we try to make the most use of the bits that we have. MicroMPX itself detects whether there is an RDS signal. It measures the level, if it's too low it will just filter it out everything above 54.4 kHz completely and not waste bits on trying to encode it. The threshold is at 1.04% - set it lower and no RDS is transferred anymore.

We could easily still send it, but there doesn't really seem to be a point - why would anyone want to encode RDS at 1%? Most receivers won't decode it anyway at that level, if it even exceeds the noise floor after going through the air. RdsSpy will decode any level it gets - I've tried it and it even works fine at 0.01%.

Upto 1.04% everything works fine. You can verify that as follows:
  • Send audio from Stereo Tool to MicroMPX.
  • Send MicroMPX output directly to RdsSpy. Turn all audio OFF (just set the FM lowpass to 0 Hz).
  • Now RdsSpy gets a completely clean RDS signal with nothing else.
  • Lower the level of the RDS signal to 1.04%.
  • Turn audio on again, send really really loud stereo audio through it upto 16.4 kHz. This does NOT affect RDS reception at all.


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 Post subject: Re: Stereo Tool 9.00
PostPosted: Fri Jul 20, 2018 4:42 pm 
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To verify whether having audio upto 16.4 is an issue, I've just tried it with Stereo Tool directly, with the RDS level set to 0.01% and full bandwidth (upto 16.4) loud audio. No reception issues at all. So, then it also can't be a problem in MicroMPX. (At least not with RdsSpy).

Interesting observation: Even with the RDS level at 0.01%, decoding still works fine with the lowpass filter set upto 17150 Hz. Which is well inside the RDS area of the audio. Even at 0.01% with loud audio going through upto 17150, reception is still perfect. At 17200 it sometimes drops a group. At 17300 it drops half of them. At 17400 reception is gone - if I raise the level to 0.03% it's nearly perfect again. At 18000 I need 0.2% RDS injection to decode everything.


Keep in mind: This test only shows what RdsSpy does, a car radio might behave differently. But what MicroMPX does now should really have no impact at all.


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