Stereo Tool

Since Beta 035, this meter no longer works correctly on my PC. I think it is just a GUI problem because I don't hear any difference. I tested ST on another device and the meter works correctly there.

We have a clipper improvement (hopefully) coming in tonight's beta.

There are 2 new things here:
- Highest vs lowest highs: stricter protection
- Reduce spikes
The first works on both L/R and composite mode, and makes clipper stages slightly stricter, which can slightly reduce volume effects on other frequencies, and on lower highs from loud higher highs.
The 2nd on, "Reduce spikes", for now only works on the composite clipper (it's for testing for now); if this works well we'll also make it work in L/R mode.

Reduce spikes needs a bit of an explanation. It may require some tweaking.
Say you have a very loud high frequency tone in your signal. Currently, that pushes everything else down:
(Cyan: Audio without that high pitched tone. Purple: Audio with that tone).
All frequencies are lower, the highest bit of the highs is about 9 dB down
The difference is also very visible in a spectral view:
With this new filter enabled, here's cyan without vs purple with again:
And the new spectrum:
This wasn't really a problem before, but recently we found out that setting "Highest vs lowest highs" a lot higher made the highs much better. But that does mean that we're pushing the highest bit of the highs (with the most pre-emphasis) very hard into the clipper, and without this new protection that causes problems.

Thanks to @Bojcha for complaining about this.
As you can see in the images above, this affects all frequencies, even the mids and lows. In this (really extreme) case the difference is about 1 dB.
Now, one thing: If you enable this, it tends to remove some of the "ringing" tones in S sounds etc which - at reasonable levels - actually sound nice. So, that's why there are strength and threshold parameters. With these 2 you can configure it such that small frequency spikes are still allowed to push things down a bit. This will likely need to be tweaked.
Finally, "Carve gap" can be used to make a gap around these loud tones. This may sound more natural, I haven't heard it yet, but there's some logic in that (preventing extremely steep filters). The effect looks somewhat like this:
This will be in tonight's new beta (042). Again, COMPOSITE ONLY for now for this 2nd filter.

This should normally have only a small impact on music, except if there are insane sounds in it, which really can happen. For example, here's half a second of a song that Bojcha sent me with a really really really weird "S" sound (I still don't know if I like it or hate it); cyan is output without this filter, purple is with this filter enabled:
I don't know how anyone manages to sing like this...

I've just been playing with settings a bit, and I think that the behavior is better if I raise "Reduce spikes higher than" a bit and raise the "Spike removal strength as well. At 2 dB and 400% (instead of 0.8 dB and 300%) I get the same protection for the weird S in this song and the high frequency tone, but less impact on other audio. But I'll leave it as-is for now to gather feedback.
The disadvantage is that more highs that push everything else down will be getting through. But maybe it's still low enough to not be a problem.
Since they are new and mostly for testing, both filters are disabled by default - so go to Advanced Clipper - Bass/Highs hole punch protection, and enable them from there. If they are really always better and we have good default values, we may enabled them by default in a future build.

A bit more info.
This is 10 minutes of music. Cyan is without the new protection, purple is with. So based on this, audio between about 6-13 kHz is reduced.
Now that seems bad. But if I zoom in on a few seconds of audio, and look at the difference signal (note: Difference, so anything here can be louder OR quieter), it looks like this:
As you can see, typically there are a lot of horizontal lines, indicating a single frequency that's reduced in the end result.
If I select one of these sections and look at the spectrum:
It's clearly not the whole highs section that's reduced, only some spikes in it. Which may still sound nice. I don't know.
And in many cases the stuff around it gets louder.

BETA042 is uploaded. Let us know what you hear!

Update: First feedback that I've received is that strength values > 100% are problematic. For > 100% we enter a different, more aggressive clipping method, which is destroying details in the highs. That probably doesn't mean that that mode should _never_ be used, but it needs to be restricted to the most extreme spikes.

Also, other reported issue: Just a loud tone gets pushed down at values > 100% if you drive the clipper really hard. That also needs to be prevented. (We will limit that mode to extreme spikes, but it still needs to not push it down).