[IDEA] Polarity Flip

[michaelagiles]

I second the request for a button to flip polarity.  For an explanation, why this is needed, see e.g. https://www.positive-feedback.com/Issue1...effect.htm
Despite being easy to demonstrate (interchange the two speaker cables at each of your speakers), this effect is not widely known and even denied by some people.

A few amps have a dedicated switch for this (like the TACT Millenium), unfortunately mine does not.  A great number of recordings suffer from reversed polarity (which allegedly sounds better when listening with headphones), see http://audiogeorge.com/the-polarity-list/

Daphile, which is only available for x86-based machines, has such a button, although hidden deep inside the menu system.

In sox the reversal can be accomplished by multiplying the volume with -1:

sox -v -1 <in-file> <out-file>

Ideally, the library would  store the information about the polarity of each track and play it accordingly without further user intervention, apart from telling the library once that this particular track needs to be inverted.

Best regards,

-- Jürgen

Hi Tim!
As a long lapsed programmer, and having no experience in any of the components of your wonderful software, I have no idea if Jurgen's idea of using  Sox to accomplish this is doable or feasible. It LOOKS simple but I really haven't a clue. This is something that was implemented in a C-Play - an early implementation of Sox upsampling etc. I assume using this Sox command. And something I have been asking for for a couple of years now - and had given up on.
Your consideration would be appreciated - but if it is simply beyond the scope of this project - so be it.
Thanks!

[Tim Curtis]

Polarity flip as I've discovered, is easily accomplished by some simple ALSA scripting. I might include it in the upcoming moOde 4.3 bugfix update.

-Tim

[koslowj]

@tim: That's sounds very promising, thanks for your efforts!

@swizzle: maybe your speakers are wired to diminish the effect.  Some speaker designs deliberately switch the polarity in some frequency ranges, but not in others.  My 3-way Audiophysics Virgos have that problem: the effect is quite small, whereas on a friend's system is is much more pronounced (with the same music).  But new speakers are on the horizon ... :-)


-- Jürgen

[koslowj]

Polarity flip as I've discovered, is easily accomplished by some simple ALSA scripting. I might include it in the upcoming moOde 4.3 bugfix update.

-Tim

Is this still on the agenda?

-- Jürgen

[Tim Curtis]

Yes, still on the TODO list but keeps getting bumped by higher priority items.

[moodenigo]

There is no balance setting in MPD but ALSA maintains individual channel volumes. You would have to use amixer or alsamixer to change the volume of an individual channel.

Would it be possible to expose this feature through moOde? It would be a *great* addition. 
For instance, there is a master volume, and then a balance control with values from -100 to 0 to 100. The positive values decrease the actual volume of the left channel (for instance, multiply by (1-balance/100)) and the negative values decrease the actual volume of the right channel (similarly, multiply it by (1-|balance|/100)). Mathematically is it easy (we can discuss this) and would be a great feature in case volume is implemented in SW (as I use it).

 Roberto

[Tim Curtis]

That approach makes sense but whats the usage scenario for a Balance control these days?

[DRONE7]

oddly proportioned room....
speaker position less than optimal as directed by the furniture overseer...
amplifier with no balance control.....
aged ears.....
et al

[Tim Curtis]

But a simple balance control is not going to compensate for these complex environmental conditions.

Something much more sophisticated would be needed for example DRC or a Man Cave ;-)

[moodenigo]

There is no balance setting in MPD but ALSA maintains individual channel volumes. You would have to use amixer or alsamixer to change the volume of an individual channel.

That approach makes sense but whats the usage scenario for a Balance control these days?

The first use case that comes to mind is recordings that have a channel unbalance. Differences of about 3db are not that uncommon. 

Second use case: Sometimes rooms have some asymmetries that cannot be completely corrected by acoustic treatment, and a bit of balance control of course is not perfect (the effect should be different for each frequency range) but can help immensely.

These are the main reasons some preamps have balance controls, but in this era of high output DACs and high input impedance buffered power amps many of us are eschewing preamps.

 Roberto
 Roberto