Stereo Tool

I've changed my AAC+ internet radio stream to 48 kbps, and at this rate the encoder uses parametric stereo.

For those unfamiliar, this means a mono channel uses about 44 to 46 of the kbps, and another channel (2 - 4 kbps) tells the decoder how to "steer" the frequencies to create an approximation of the original stereo image. It works pretty well, but I'd like to make it as easy as possible on the encoder.

I've tried expanding the stereo, which made the artificial quality a lot more obvious (large chunks of a frequency band jumping to one side or another, leaving the other side sounding muted, etc. If I reduce the stereo image too much, the encoder gives up and the signal becomes basically mono.

One setting I've considered is the Matrix Mode, which should keep the L-R content about the same level all the time if I understand it properly.

I couldn't find any info in the help section about this tool. Will it help the encoder to best use those few bits to create a great stereo image? The default on "reduce stereo" is 50%... should this be higher or lower? What about L+R to L-R mix? (Default is 0%.) ...and what is "Max Not Mix?"

I keep the azimuth correction on all the time (I'm playing pop from the 1980s)... is that likely to help, or hurt? "Stereo Boost," "Stereo Image"... could any of these help?

I also might mention here, I'd love the option to "center bass" without turning on the entire stereo enhance section.

Parametric stereo certainly improves the sound quality of low bandwidth streams, but it's a challenge to process!!

_________________
Gene Savage
BlackLight Radio
https://BlackLightRadio.com
Tulsa, Oklahoma USA

There is a bit of info about Matrix Mode here: http://help.stereotool.com/7.40/agc.shtml

You should definitely leave AZIMUTH correction on! That helps a lot in cases where there are AZIMUTH issues, and it does nothing otherwise.

The Stereo Image section might be very useful for what you're doing, but it causes quite bad artifacts. Fortunately, I have improved it 2 days ago - so you need to get the latest 7.41 beta release: viewtopic.php?f=14&t=5456&start=30

I have no experience with this mode, but based on what you are describing I think 3 sliders in Stereo Image might be useful:

Image phase amplifier
This increases OR DECREASES phase differences. If there are phase differences, when you convert audio to mono you loose some sounds. So I'm guessing that AAC will not sound very well if there's a lot of phase differences in your signal. Try reducing this one.

Image phase amplifier maximum angle
Limits the maximum amount of phase difference. Might also work, and if you don't set it all the way to 0, it has less effect on the audio.

Image width amplifier
This moves sounds further away from the center or towards the center, without affecting the phase. This *might* be a safe way to increase stereo separation.

Please let me know your results - I'm really curious!

Well, I ended up abandoning parametric stereo entirely. The imaging wasn't pleasing with normal stereo programming, when I reduced the stereo phase information the stereo image collapsed (apparently the encoder depends on phase info heavily to decide what to present in stereo) and adding in the matrix-style processing created a merry-go-round effect that one listener described as making them "nauseous."

It is no weakness in Stereo Tool; it is the limitations of Parametric Stereo.

At this time I've shut off all stereo enhancement and am feeding a true stereo stream, and it sounds wonderful.

I'll ask a question about the latest betas in its own thread. Thanks for all the information!!

_________________
Gene Savage
BlackLight Radio
https://BlackLightRadio.com
Tulsa, Oklahoma USA