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Overshoot
https://forums.stereotool.com/viewtopic.php?t=32		 Page 1 of 2
Author:  SuperH [ Mon Jun 09, 2008 2:55 pm ]
Post subject:  Overshoot
I've been using Stereo Tool for a while for my Internet radio stream (that I use for my and my friends' entertainment mainly), and to control aacPlus CODEC artifacts with stereo image manipulation, and I have a question about "HARD LIMIT". My understanding is that "HARD LIMIT" should flatten all peaks with a fast attack with no discernible overshoot. Unfortunately, I cannot seem to combat this issue -- I am getting substantial overshoot at times.

I have attached a waveform illustrating this.
Image

Here's an example of what I'm looking for in terms of overshoot (look at the blue upper waveforms). This is a sample taken from XM's "The Heat", processed by "Neural Audio".
Image

For comparison purposes, I've aligned the tracks off of the albums themselves (that I transcoded into MP3s) with what XM was playing at that time -- XM's version is shown up top -- my comparison (unprocessed) is shown at the bottom.

I love Stereo Tool, but I cannot seem to get past that one problem! Thanks in advance!
Author:  hvz [ Mon Jun 09, 2008 4:53 pm ]
Post subject:  Re: Overshoot
There are several things that can cause overshoots to occur in this setup.

If you feed the output of Stereo Tool through an AAC (or any other lossy) encoder, the wave form changes - and some peaks will get louder. To accomodate for this, lower the Post Amp to slightly below 1 (the Internet Radio presets have the Post Amp set to 0.93 - for lower bitrates, you might need even lower values).

Post Amp is performed AFTER the hard limiter. If you look at the output volume bars in Stereo Tool, if Hard Limit is enabled they should never peak above the level that you set in Post Amp (0.93 means that never more than 93% of the output level bar may be filled).

If the output bar sliders do indeed stay below the threshold, the overshoots are caused after the Stereo Tool processing (eg. probably in the AAC encoder).
Author:  SuperH [ Mon Jun 09, 2008 5:46 pm ]
Post subject:  Re: Overshoot
I've noticed this prior and post encoding. My output is set to 0.95 -- and I've never seen the output levels exceed a short distance from the end caused by the 0.95.
Author:  hvz [ Mon Jun 09, 2008 6:25 pm ]
Post subject:  Re: Overshoot
Does that mean that the problem is solved now?
Author:  SuperH [ Mon Jun 09, 2008 6:40 pm ]
Post subject:  Re: Overshoot
No, the problem happens with the setting at 0.95. I'll investigate it further when I get back to the console. I will post an update later on tonight based on my findings! :)

I'll check it pre-encoder.
Author:  SuperH [ Tue Jun 10, 2008 1:32 am ]
Post subject:  Re: Overshoot
Overshoot still appears to be there pre-encoder.
Author:  hvz [ Tue Jun 10, 2008 3:00 am ]
Post subject:  Re: Overshoot
Most important question: Do you see overshoots when looking at the output indicators of Stereo Tool? They display the maximum value that Stereo Tool returns to the application - no overshoots in this display means no overshoots in the output signal from Stereo Tool.

Could you post your settings here? Just save to a .sts file, then copy the contents of the file (it's just plain text) in a post here.

Also, which version of Stereo Tool do you use? And in which program do you use it? When looking at the output volume indicators, do they also show overshoots?

I just ran a test with extremely agressive settings, Post Amp at 0.95. When looking at the waveform that came out, I found this:
Image
which looks perfect. Please send me your .sts file so I can run the same test using that file.

By the way - are you using SAM? Because if you are, the built-in SAM AGC might be the cause of the problem. (You should turn it off)

Thanks,
Hans
____
Author:  hvz [ Tue Jun 10, 2008 3:10 am ]
Post subject:  Re: Overshoot
Side note: I just did a quick test with an MP3 encoder at 128 kbit/s, and even when setting Post Amp to 0.80 I was still getting very frequent overshoots. I will adjust the internet radio presets to 0.80 for this in the next version.
Author:  SuperH [ Tue Jun 10, 2008 6:50 am ]
Post subject:  Re: Overshoot
I am using SAM. The built-in AGC should be off. The overshoots aren't a huge issue, but I do see them.

I am using version 3.14. The output volume indicators do not show overshoots. I almost wonder if it is how I am capturing the waveform...

Thank you!

Here is one of the settings files I've witnessed the phenomenon on:

[Common]
Pre amplifier=3.300000191
Post amplifier=0.949999988
Extra loudness=1
Hard limit output=1
Downsample very high input sample rates to near 44.1 kHz=1
Mode=Advanced
[Noise Gate]
Enabled=1
Difference=0
Noise level=1.5
[Singleband Compressor]
Enabled=0
Difference=0
Maximum volume=10
Maximum value=32767
Attack speed=0.999998987
Decay speed=0.999000013
Above Top Limiter=1
[Pre Compressor]
Enabled=1
Difference=0
Delay enabled=0
Maximum volume - Band 1=25000
Maximum volume - Band 2=15000
Attack speed - Band 1=0.000003152
Attack speed - Band 2=0.000002737
Decay speed - Band 1=0.040594164
Decay speed - Band 2=0.026004046
[Multiband Compressor]
Enabled=1
Difference=0
Delay enabled=0
Very high quality enabled=1
Maximum volume - Band -1=7200
Maximum volume - Band 0=8310
Maximum volume - Band 1=8810
Maximum volume - Band 2=7630
Maximum volume - Band 3=5930
Maximum volume - Band 4=3730
Maximum volume - Band 5=2750
Maximum volume - Band 6=3100
Maximum volume - Band 7=3750
Maximum volume - Band 8=1750
Attack speeds linked=0
Attack speed - Band -1=0.000002737
Attack speed - Band 0=0.000002737
Attack speed - Band 1=0.000015691
Attack speed - Band 2=0.000015691
Attack speed - Band 3=0.000015691
Attack speed - Band 4=0.000015691
Attack speed - Band 5=0.000015691
Attack speed - Band 6=0.000132422
Attack speed - Band 7=0.000132422
Attack speed - Band 8=0.000132422
Decay speeds linked=0
Decay speed - Band -1=0.001828427
Decay speed - Band 0=0.001828427
Decay speed - Band 1=0.000139355
Decay speed - Band 2=0.000139355
Decay speed - Band 3=0.000139355
Decay speed - Band 4=0.000139355
Decay speed - Band 5=0.000139355
Decay speed - Band 6=0.000139355
Decay speed - Band 7=0.000139355
Decay speed - Band 8=0.000139355
Above Top Limiter=1
Clipping enabled=1
Postprocessing enabled=1
Relative clip position - Band -1=1.500000238
Relative clip position - Band 0=1.500000238
Relative clip position - Band 1=2.508771658
Relative clip position - Band 2=2.508771658
Relative clip position - Band 3=1.500000238
Relative clip position - Band 4=1
Relative clip position - Band 5=1
Relative clip position - Band 6=-1
Relative clip position - Band 7=-1
Relative clip position - Band 8=-1
Final limiter value=0.258100003
Final limiter decay speed=0
Final limiter clipping=0.600000024
Equalizer enabled=1
Equalize before multiband-compression=1
Equalizer position - Band -1=2.508771658
Equalizer position - Band 0=2.508771658
Equalizer position - Band 1=2.508771658
Equalizer position - Band 2=2.508771658
Equalizer position - Band 3=1.702702761
Equalizer position - Band 4=1.105262995
Equalizer position - Band 5=0.600000024
Equalizer position - Band 6=0.503759503
Equalizer position - Band 7=0.408450603
Equalizer position - Band 8=0.25
[Stereo]
Enabled=1
Delay enabled=0
Difference=0
Center bass=1
AZIMUTH limit=60.979999542
AZIMUTH change speed=0.200000003
Image phase amplifier=1.399999976
Image phase amplifier maximum angle=130.5
Image phase amplifier maximum separation strength=65.849998474
Image width amplifier=1.200000048
Extra phase shift=0
Mono or stereo only=-0.659999967
[Channel Delay]
Enabled=0
Left Delay=0
[Output Filter]
Enabled=1
Lowpass filter=15000
[Final Pre-Limiter]
Enabled=1
Difference=0
Pre-amp=1.708543897
Response time=0.400000006
[Final Limiter]
Enabled=1
Difference=0
Pre-amp=1.330095887
Response time=0.0125
[FM Transmitter]
Enabled=0
Pre-emphasize=0
Pre-emphasis time=50
Output is pre-emphasized=0
Stereo encoder enabled=0
RDS encoder enabled=0
RDS PS text=2s:STEREO/2s:TOOL/<1=1.5s,2..-2=2t,-1=1.5s:WWW.STEREOTOOL.COM
RDS RadioText text=60s:Stereo Tool: Professional Audio Processing - http://www.stereotool.com/30s:Stereo Tool by Hans van Zutphen, 1999-2008 - http://www.stereotool.com
RDS PTY=0
RDS PI=65535
RDS Alternative frequency 1=0
RDS Alternative frequency 2=0
RDS Alternative frequency 3=0
RDS Alternative frequency 4=0
RDS Alternative frequency 5=0
RDS Alternative frequency 6=0
RDS Alternative frequency 7=0
RDS Alternative frequency 8=0
RDS Alternative frequency 9=0
RDS Alternative frequency 10=0
RDS Alternative frequency 11=0
RDS Alternative frequency 12=0
RDS Alternative frequency 13=0
RDS Alternative frequency 14=0
RDS Alternative frequency 15=0
RDS Alternative frequency 16=0
RDS Alternative frequency 17=0
RDS Alternative frequency 18=0
RDS Alternative frequency 19=0
RDS Alternative frequency 20=0
RDS Alternative frequency 21=0
RDS Alternative frequency 22=0
RDS Alternative frequency 23=0
RDS Alternative frequency 24=0
RDS Alternative frequency 25=0
RDS TP=0
RDS TA=0
RDS Music=1
RDS Artificial Head=0
RDS Compressed=1
RDS Dynamic PTY=0
RDS RadioText Enabled=1
RDS ClockTime Enabled=1
[Direct soundcard access]
Enabled=0
Device ID=
Volume=1
Buffer size=1
Send to Winamp=Nothing
[Low latency output]
Enabled=0
Device ID=
Volume=1
Buffer size=0.079999998
Author:  hvz [ Tue Jun 10, 2008 10:22 am ]
Post subject:  Re: Overshoot
I've tried your settings here in Winamp, and I'm not getting any overshoots.

Which of course leads to the question: How did you measure your output?

In SAM, make sure that AGC is turned off for ALL processing channels, as described in http://help.stereotool.com/stereo_tool_and_sam3.shtml - make sure that they are ALL set to Bypass.
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