Stereo Tool
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Low latency secondary input (microphone)
https://forums.stereotool.com/viewtopic.php?t=853		 Page 17 of 75
Author:  Bojcha [ Tue Dec 29, 2009 9:22 pm ]
Post subject:  Re: Low latency secondary input (microphone)
it seems that many people follows this topic .. link is only for 10 times download .. and expired after 3 hours..

clipping:
http://www18.zippyshare.com/v/18088133/file.html

nrbol:
http://www18.zippyshare.com/v/27928716/file.html
Author:  hvz [ Wed Dec 30, 2009 3:42 am ]
Post subject:  Re: Low latency secondary input (microphone)
Bojcha: I've downloaded both files and I heard what the problems are. Will try to fix them tomorrow.

Clipping can probably be fixed by clipping less tightly.

I'll have to check what's causing the stereo boost rumbling, I did a measurement here with silence on one channel as input and the output contained absolute silence. (In your original, is the channel that's silent absolutely silent, or does it contain - for example - an offset?)
Author:  hvz [ Wed Dec 30, 2009 3:49 am ]
Post subject:  Re: Low latency secondary input (microphone)
I'm currently building an update with the following changes:
- Fixed a small bug in the highpass filter that may have caused some artifacts.
- Fixed a bug in the Hard Limit filter for FM transmitters; probably no or very little effect on the output.
- Bug fix: Loudness indicators fixed.
- Bug fix: Very deep bass distortion protection DIFF is working properly now.
- Stand alone version: 2nd input channel removed (for now)
- In Low Latency mode, If Multiband is turned on and the highpass filter is used at frequencies between 12 and 46 Hz, the multiband filter gives the bass a slight boost.
- Replaced Lo/Mid/Hi quality and latency Low/Normal by a separate window where the latency can be selected (512, 1024, 2048, 4096 samples), and several settings are present that determine the output quality. See below.
- Changing quality and latency settings on the fly should work now without problems.

About the output quality:
Code:
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       /     \
      /       \
     /         \
           _____
          /     \
         /       \
        /         \
Latency
As you can see in the drawing above, the audio is processed by Stereo Tool in chunks of a certain size. This size is either 512, 1024, 2048 or 4096 samples (per channel).
4096 corresponds to Normal Latency in the previous version, Low Latency is 1024 samples.

Steepness
To avoid sudden cut-offs of the sound (which sound like a loud 'click' and will therefore damage the rest of the sound as well), a "window" is placed over each chunk, where the sound gracefully drops to 0.

The part of the audio where the volume drops to 0 cannot be used because it contains too many artifacts. So the steeper the sound drops to 0, the bigger the part of the sound is that can be used. But this comes at a cost, the steeper the slopes are the more artifacts will occur in (very) low frequencies.

Overlap size
Near the slopes, some artifacts might already be present, especially at very low frequencies. Also, when Loudness is used, different chunks may be processed very differently. In other words: They might not match perfectly.

Just concatenating the flat areas would often lead to loud clicks in the sound (comparable to 'blocks' that you can see in videos with low bitrates). So instead, it's necessary to use some 'overlap' between chunks.

The bigger the overlap is, the better the sound will be - but the CPU load will also increase a lot. (For example, for maximum overlap, every sample must be in the flat part of 2 chunks, which means doubling the CPU load!).

The effect is the biggest on very low frequencies, and when using low latency settings (because in low latency modes, the chunks themselves are very small, so the overlap size is also small).

Basically, if the overlap area gets bigger, both the amplitude and the frequency of mismatches between chunks go down.


In the previous BETA3 version, Normal mode used an overlap of 25% and slopes of 75% in Normal quality mode, 50% and 100% in High quality mode.
Low Latency mode, the overlap in Normal quality was 50%, High quality 100%.
Author:  hvz [ Wed Dec 30, 2009 6:43 am ]
Post subject:  Re: Low latency secondary input (microphone)
Uploaded!

The links again:
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
Author:  hvz [ Wed Dec 30, 2009 7:44 am ]
Post subject:  Re: Low latency secondary input (microphone)
Extra TODO: Try to reduce bass rumbling in extremely low latency mode. (Probably not possible, but if it is it would greatly improve the sound quality).
Author:  Bojcha [ Wed Dec 30, 2009 5:19 pm ]
Post subject:  Re: Low latency secondary input (microphone)
eXtra!
That's mean that with "block overlap" over 50% we can produce better quality then old (HI) mode ? Ofcourse with strong CPU.

I just tryed on one AMD PC .. can't wotk with ALL ON..(block overlap 50%) and CPU is at 55-60% both cores ... but that's old AMD vs ST problem .. later i'll try on Intel e5200/5300
Quote:
In your original, is the channel that's silent absolutely silent, or does it contain - for example - an offset?
Absolutely silent, muted channel from SoundForge and played from winamp. maybe winamp do something.
Author:  hvz [ Wed Dec 30, 2009 6:24 pm ]
Post subject:  Re: Low latency secondary input (microphone)
Quote:
eXtra!
That's mean that with "block overlap" over 50% we can produce better quality then old (HI) mode ? Ofcourse with strong CPU.
If "Old" = previous BETA3, then yes. But I doubt the difference will be noticeable - if you set it lower it doesn't change much either, and the bigger the overlap gets the less effect it will have. In low latency modes it does clearly have an effect though.
Author:  hvz [ Wed Dec 30, 2009 7:44 pm ]
Post subject:  Re: Low latency secondary input (microphone)
Stereo Boost silent channel problem found and solved. This has apparently also reduced the "bass rumbling" problem (it's not gone, but it's less present.)
Multiband clipping problem found and solved.

New version is coming in about an hour!
Author:  hvz [ Wed Dec 30, 2009 10:56 pm ]
Post subject:  Re: Low latency secondary input (microphone)
Uploaded!
Author:  hvz [ Wed Dec 30, 2009 11:09 pm ]
Post subject:  Re: Low latency secondary input (microphone)
OOPS! It wasn't uploaded! It is now.
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