Hi all,
I would like to configure an audio track like this:
- Mono for frequencies < 200 Hz
- Stereo for frequencies > 200 Hz.
Is there a plugin to do this?
[Ardour 8.1 on Linux]
Thank you,
a.
I don’t know if there is a plugin labeled specifically with that feature, but you can convert to mid-side, and reduce low frequencies in the side channel with whatever EQ plugin you like, possibly increasing slightly the low frequencies in the mid channel to compensate if needed to maintain balanced sound.
These are concepts I don’t know… 
Any links explaining how it works?
Thank you,
a.
Blue Lab Stereo Width: BlueLab Audio Plugins : BlueLab : Free Download, Borrow, and Streaming : Internet Archive
MONSTR: MONSTR | White Elephant Audio
I’d say the easiest way is to use the “Parametric Equalizer x16 MidSide” from the LSP plugin suite. Just keep sure to select the correct filter list in the (orange) marked drop-down list (“Filters Side 0-7”) and then adding a low-pass filter at 200Hz there would be an example solution to your question.
This is a link from izotope, so has a pretty good introduction to how you would use M-S with plugins:
https://www.izotope.com/en/learn/what-is-midside-processing.html
The readme says “Currently only macOS is supported.”, but I compiled and am using it without problems on Linux.
Did you test it?
I was going to include it in my suggestions above and I took the liberty to actually test them before posting.
bw-utilities BASS MONO doesn’t work as good as my other suggestions, is not able to make a stereo signal really mono, at best is just reducing stereo width a bit.
Converting to Mid-Side and applying eq to the side channel would work fine if the source was recorded with XY mic-setup (or, obviously, MS). Or if it is the result of mixing mono channels using “pan” to do the stereo image.
But if the source was recorded with mics which are not located in the exact same spot, lie ORTF or AB micing, then I guess there will not be that much in the Mid-channel when you convert to MS. The low frequencies will also be in the side channels. And if you remove them from the side channel, you remove them completely from the result.
Mathematical definitions:
Mid = Left + Right
Side = Left - Right
Mid is just another term for “mono”, and what mono should be if done correctly.
Side is sometimes what “mono” ends up as, when people stuff a 1/4" phone plug into a 1/4" socket just because it fits. Then they wonder why the bass and vocals went away or it just sounds “weird”. If you’re going to use 1/4" plugs, you really need to know for yourself what you’re doing, because that exact same connector is used for almost everything! And those uses are NOT directly compatible with each other!
Anyway, with that PSA out of the way, Mid+Side encoding is incredibly useful, not just for this application, but for data compression as well. A lot of stereo encoders convert to M+S first, and then allocate more bits to the sum than to the difference. The decoder/player then reverses the entire process: decodes the M+S signal first, and then converts it back to stereo:
Left = Mid + Side
Right = Mid - Side
All of its uses come from our stronger perception of the sum than of the difference. We notice “what” more than we do “where”. If there’s a strong stereo effect going on, sure we’ll notice that, or we might notice that certain things are “sitting” off to one side or the other, but most of what we concentrate on is the overall sound, and that’s mono.
Thus, the Mid signal can be processed as the “front and center” thing, while the Side gets a different treatment as more of an “effects channel”. Compression, EQ, reverb, etc. Then convert back to stereo. It creates a different sound to do that, than to try and do everything in just mono or stereo.