[IDEA] Polarity Flip

[koslowj]

Hi Tim,

I've since found the following in the mail archives for alsa-users:
https://www.mail-archive.com/alsa-user@l...17740.html
If this doesn't help, I can ask in the other forum.

-- Jürgen

[Tim Curtis]

Yes, please post in diyAudio because it appears that a LADSPA plugin may exist to reverse polarity. The challenge for me is that w/o any explanation of which specific plugin or how it works its going to be difficult to justify spending time trying to figure things out.

-TIm

[energyi]

Take headphones off head, spin 180 degrees and put them back on.

[swizzle]

I don’t find polarity flipping all that useful (my dac has a switch, it’s never used) but there’s an interesting theory involving flipping the polarity of one channel as it goes into the amp before flipping it back as it goes into the transducers:

https://www.superbestaudiofriends.org/in...rsal.2942/

[Tim Curtis]

Interestingly, this post at diyAudio provides an ALSA example that can be used to perform polarity inversion on both L/R channels.
https://www.diyaudio.com/forums/pc-based...-alsa.html

I'll be happy to code something for testing. It looks like MPD will need to be restarted if the polarity of L/R channels is changed.

-Tim

[swizzle]

If I’m reading that right and the range is 0 - 1 for channel volume and negative denotes a polarity flip seems like that could be interesting to expose in an advanced panel that lets the user control max l/r volume and/or polarity per channel. I think the original idea was per song but that seems more like an mpd enhancement since it’d have to be in their db.

[TheOldPresbyope]

If I’m reading that right and the range is 0 - 1 for channel volume and negative denotes a polarity flip seems like that could be interesting to expose in an advanced panel that lets the user control max l/r volume and/or polarity per channel. I think the original idea was per song but that seems more like an mpd enhancement since it’d have to be in their db.

Surely a per-song solution is infeasible.

[Tim Curtis]

AFAIK, doing it on-the-fly while song is playing or doing it on a per song basis would require the feature to be part of MPD itself. Maybe someone could could post a feature request in the MPD Git :-)

There does seem to be some confusion as to whether the ttable coefficient is performing a phase shift or polarity flip. I think it must be performing a polarity flip when its negative because the coefficient itself represents a volume %. Its probably just confusion over the terminology.

https://www.diyaudio.com/forums/pc-based...-alsa.html
https://www.justmastering.com/article-ph...larity.php

[TheOldPresbyope]

AFAIK, doing it on-the-fly while song is playing or doing it on a per song basis would require the feature to be part of MPD itself. Maybe someone could could post a feature request in the MPD Git :-)

There does seem to be some confusion as to whether the ttable coefficient is performing a phase shift or polarity flip. I think it must be performing a polarity flip when its negative because the coefficient itself represents a volume  %. Its probably just confusion over the terminology.

https://www.diyaudio.com/forums/pc-based...-alsa.html
https://www.justmastering.com/article-ph...larity.php

I'd be willing to bet the pcm route type plugin does only polarity inversion (aka flip) but the answer lies in the source code. I haven't found the source for pcm route plugin yet, just a bunch of function references.

[Tim Curtis]

Looks like in the diyAudio thread that @phofman confirmed that its performing polarity inversion :-)