Stereo Tool

Note: I'm working on a declipping filter (was doing that a few months ago, and picked it up now). See viewtopic.php?f=16&t=3595&start=15 . If you are using some declipping filter yourself, I'm curious about comparison results.

From what i've seen in some datasheets i see a 80 KHz LPF before the stereo decoder. So that means the RDS signal isn't filtered out. I could not find a datasheet with a steep filter which filters out the RDS before stereodecoding. In DSP versions they could use this probably.
When i look at the Left or Right output of my tuner i also see RDS signals around the 19 kHz pilot tone. But under normal circumstances you can't hear it because it's quite low.
The RDS decoder chip however has a very steep bandfilter so also no problems there for the RDS decoding part.

The stuff you see around the 19Khz is intermodulation with the RDS signal. Normally the reason why they choose 57KHz is because it is the 3rd harmonic of 19KHz and shouldn't cause interferance.
Since RDS is using baseband modulation with a surpressed carrier (57KHz is actually not there) and is being modulated with 1187.5bit/s sec you are likely to get interferance in some cases because of the modulated psk. 19-1.1875 = 17.8KHz and 20.18KHz

The RDS substraction/filtering is done in most RDS IC's itself
http://home.scarlet.be/~wijnherm/tda7330.pdf

The reason why they will not really filter sharply below the RDS freq is because the phaze shifting of the filters will destroy the stereo separation.

@Luke thanks for some more detailed explanation.
@Hans do you still think this feature is useless? If so could you explain why.

Orban has that feature for long time, i guess new Omnia too.

In my expirience, there is a difference at all my tuners between HPF filter at 15,5 and 17,5 kHz.

Did the corrected beta get posted? I could not find it.

_________________
J0HN II

I think Hans has forgotten, the BETA was not posted. I think you mean LPF instead of HPF.

yea... LPF

BETA620-018:

- VST window issue fixed (Sorry! Forgot to post it earlier... )
- Declipping filter added. Note: If you enable this filter, you'll get a 'This sound is processed by Stereo Tool' played over it every 60 seconds! The reason for this is that I want to release this filter as a new stand alone application as well, since it really seems to outperform all the well-known declipping filters (and on top of that it has a low latency!). I still have to decide how to put this into Stereo Tool.

Note that declipping uses a lot of CPU processing power (I'll make that configurable later).

The filter can be switched on or off at the right of the input level slider.

The 'maximum peak restore' slider does not work yet (dunny why, will check).

IMPORTANT: Set the 'clipping detection' level low enough such that ALL the clipped samples are recognized as being clipped (for a CD that's easy, 32767 should suffice, but for an MP3 you'll need to set it a bit - even upto 10%! - lower).

Hint: You can see that the declipping filter is working by comparing the input and output levels with NO other processing enabled.

IMPORTANT: Declipping can currently NOT be combined with non-phase linear highpass filtering!!!

Samples that are incorrectly seen as not-clipped (level set too high) can have a big effect on the audio.
Samples that are incorrectly seen as clipped (lever set too low) make things harder because basically Stereo Tool must treat them as if they are clipped at the selected level. So basically you add extra clipping before removing it.

Later I'll add some code for dynamic clipping detection. (Something with a histogram I guess).


Winamp DSP plugin: http://www.stereotool.com/download/dsp_ ... 20-018.exe
Stand alone version: http://www.stereotool.com/download/ster ... 20-018.exe
VST version: http://www.stereotool.com/download/vst_ ... 20-018.dll
VST version (No SSE2): http://www.stereotool.com/download/vst_ ... 20-018.dll
Command line version: http://www.stereotool.com/download/ster ... 20-018.exe
Linux command line version: http://www.stereotool.com/download/ster ... ETA620-018 NOT AVAILABLE
Linux GUI version: http://www.stereotool.com/download/ster ... ETA620-017 NOT AVAILABLE

TODO:
- Fix loading changed multiband frequencies
- Add buffer and filter for SCA output (SCA1 ok, SCA2 ok)
- Finish AGC improvement - make mono value configurable (replace checkbox by slider) 1 hour --> NO, not needed - anything else needed? -> NO
- Fix Punch
- Check what to do with new filters (such as bass AGC) - keep them, remove them, change them? --> KEEP
- Save new BASS_AGC setting in VST mode
- Loudness: Annoying cracking sound in bass. Slightly present in 5.00, worse in 6.00, maybe even worse in 6.10. Only when bass is too loud. Much worse than in Final Limiter (at same input level!) - so this clearly indicates a bug. Most likely cause: The filter that was added to remove bass artifacts....... - No, it's the louder bass. But it can be fixed by changing some settings. Default settings updated, and behavior for 'not Very strict' improved. Also Deep bass boost and Very deep bass protection are enabled for latency 512 now.
- Finish declipping filter.
- Add highpass filter for stereo signal (will cause a lot of extra latency!)
- Update presets? (BASS_AGC etc.)
- Change version number 1 hour
- Release 1 hour

Could you add a line to the scopes display for setting the correct value?