Stereo Tool

Optimization TODO list:
- Chain() function still uses 15% of the total CPU power. Rewrite clipping filters in SSE2, then re-check. --> No effect (0.16%)... But most of it is in Hard Limit + Loudness.
- Trumpet: Rewrite to use only a single pass. ■ DONE
- OvershootBands filter (used for Pre Limiter and Loudness) accounts for about 8% of the total CPU usage. That's quite a lot. 1: Combine Pre Limiter with Pre Limiter processing itself. 2. For the 2nd one, use FFTs (which are not really cheap) instead of the current frequency splitting filter. ■ Postponed until the new single channel RMS based Pre Limiter is finished
- Multiband: Currently only 3 assembly instructions account for 30% (!) of the total Multiband CPU usage. Check if that can be solved (probably not...).

Just posted another minor performance improvement (but it's so small I have trouble even measuring the difference).

Hi Hans,
i don't know should i post this i new topic or here... I know there is still work for new version of Stereo tool. but if you wish to put this in todo list.

It's about prelimiter!
I have very big problems with certain songs. it's mainly songs where voice is higher level then music.
What actualy happen is when singer is over music and his voice peek level is around 400-1000Hz .. it kills whole band under that. I found that it's because prelimiter.
When i turn off prelimiter and set post-amp to proper level so multiband can work as usual ..everything is much better.
I searched how on other processors "AGC" works and found that most of them mainly have 1-band AGC, with agressiv peek limiting and on most of them one interest option called "Gain Threshold"
It's very usefull and very simple option and can be used on multibands too.

From omnia user manual:
The Gate Threshold control sets the level at which gating of the AGC occurs, “freezing” the gain during short
pauses. Correct adjustment of this control helps to minimize “pumping”, and the increase of background noise
during pauses in programming.

I think this can help StereoTool to work much better.
...or just is it possible to have option for 1-band Prelimiter?

At the dutch forum i've told hvz this about a ACG already, so he knows a little bit of it.
I think too that a ACG might be better then this pre limiter, or make, like you said bojcha, the pre limiter 1 band.

Actually, in this case the pre limiter is already functioning roughly as a 1-band filter: If the lows get dropped, I'm taking down the highs as well to avoid 'shrill' sounds.

If I read what this "gating" does I don't see how that would help in this case? Basically, there's a very loud tone at around 400-1000 Hz which takes down the rest of the sound. Since it's a very loud sound I need to do something there.

I was just googling a bit and I found this:
if the audio falls below the threshold the compression won't try to increase the gain until it's above that point again.

So, if there's little sound, I should do nothing (not increase the volume at all)... Well, if the input is relatively constant already that might indeed improve things (after silence, the volume won't have increased to the maximum so I don't have to drop it very rapidly - and that should also help in songs with short bursts of sound with silence in between) - but I don't see how that solves the problem with the voice which causes a drop in lower frequencies?

Bojcha, if possible, could you try to describe what you expect to happen in this case? If I understand what you want I can probably implement it... But right now I don't see how this is going to help. (For the problem that you describe, that is. Gating seems to be very useful and I'll definitely put it on my todo list. Did I ever mention that I'm not an audio processing expert and that I only wrote Stereo Tool to get some experience in using Visual C++ ?)

(Edit: Gating + AGC have been added to the todo list. Fortunately now the CPU load is so much lower I have room for extensions...)

Addition: I just realized why you say that using a single band would improve things. I think you're right - right now the lows are dropped due to the loud tone, and the highs follow the lows. If everything was dropped simultaneously, the presence of the high frequencies would (slightly?) reduce the effect.

The fact that I'm already letting the highs follow the lows probably indicates that it's a good idea to use a single band.

In the mean time, here's another update. I rewrote the Trumpet filter.

- CPU load is 2% lower.
- I found a bug in the filter that caused distortion in loud high frequencies (this has probably been there since version 4.01 or so). Fixed. Loud highs might be slightly softer now (-0.1 dB), but should sound cleaner.

Hi Hans,
You are right .. this gating has nothing with the High voice on mids and drop on whole 1st band in Pre-Limiter.
This "Gate Treshold" is just wish. And 1-band Pre-Limiter is what i think is better in case "loud mids drops lows"

"Gate Threshold" actually signals to bands (prelimiter+multiband, separalty to all bands) when to stop moving - Freeze Bands. So if pause happen (~0.1>sec) bands will be freezed to their positions and not going up. So when audio is back it will again start to move from their previously position. And there is a setting for how much threshold will this gate detect (what i see on most processors that option is some default number) This is very good for dry voices but for music too.

1-band PreLimiter...
I think it will be better but it will not work so good with this settings from 2-bands.. maybe it will need faster release and attack and better peek control.

Here is one example:
http://www47.zippyshare.com/v/95369337/file.html
attention to words Never Alone!

I always like Stereo Tool because is more natural sound then other famous processors Like Omnia, Optimod .. etc ...
So only this small things is missing.

I made a very quick hack and this song does indeed sound better (warmer and more constant) with a single band 'pre limiter'. I'm building all versions now, will upload them in an hour. Don't expect too much: I've only added a few lines of code so that in the Pre Limiter the content of the 2 bands is merged so they are identical. But - at least based on this one song - this is definitely the way to go.

(I do have the impression that I hear a bit more distortion though, but maybe that's because the sound is also louder. Will check this later - it's time to finish up for tonight). Edit: Probably caused by my headphones...

Edit: I also hear improvements in other songs (some tracks that start with a loud bass-kick sounded a bit 'thin' because the bass was dropped a lot compared to the highs - that's now no longer the case).

Edit #2: The trumpet bug fix seems to have greatly improved the sound at lower latencies! (Highs sound much cleaner at low latencies than before).

"Singleband" AGC: First attempt uploaded as BETA3 (NOT 3A!):
Winamp DSP plugin: http://www.stereotool.com/download/dsp_ ... _BETA3.exe
Stand alone version: http://www.stereotool.com/download/ster ... _BETA3.exe
VST version: http://www.stereotool.com/download/vst_ ... _BETA3.dll

Please let me know what you think.