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Polarity inversion
08-02-2015, 22:53
Post: #1
Polarity inversion
Does make any sense that MinimWatch can set whether MinimServer should provide the requested audio file with polarity inversion or not?

Thanks
-R
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08-02-2015, 23:02
Post: #2
RE: Polarity inversion
(08-02-2015 22:53)robertopisa Wrote:  Does make any sense that MinimWatch can set whether MinimServer should provide the requested audio file with polarity inversion or not?

Thanks
-R

MinimServer serves the exact contents of the audio file unless MinimStreamer transcoding is active.

Polarity inversion was provided as a transcoding option for FLAC files a long time ago. I removed this when transcoding was extended to other filetypes because there wasn't a practical way to generalise this. No-one commented on this change, so I presume no-one was using this capability.

If you want to invert the polarity of a file, you will need to convert it offline.
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10-02-2015, 22:35
Post: #3
RE: Polarity inversion
Good that people does not hear polarity inversion.
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05-01-2021, 04:12
Post: #4
RE: Polarity inversion
Hi, I'm new here, since I'm looking for exactly this feature. Has anything changed since 2015? I'm presently streaming via MPD from an SOTM sms 200 ultra neo, which comes with the option of using minim-server. The music library is on a local NAS. Unfortunately, my DAC+Amp (Lyngdorf TDAI 2170) does not have a dedicated polarity switch, as do some other amps, and I'm looking for a software solution. (The Lyngdorf is capable of handling 32 bits at 384 MHz via USB.)

Apparently, Roon does have this feature, but first I would like to explore Minimserver/-streamer. The majority of material is encoded as FLAC, a few DSD-files are streamed via dop, as my DAC doesn't accept that format natively. If needed, Minimstreamer might be used to transcode to FLAC beforehand.

The option of switching polarity on the fly would help enormously in deciding which files are inverted, before fixing them offline, at least the FLAC-files

In order to offload the work from the SOTM sms 200, I could also try to move Minimserver and Minimstreamer to a dedicated Odroid N2.

-- Jürgen

P.S. In case you have difficulties hearing a difference when flipping the polarity, you may have 2-way or 3-way speakers, where the polarity is already flipped for some frequency ranges, but not for others.
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05-01-2021, 14:59
Post: #5
RE: Polarity inversion
(05-01-2021 04:12)koslowj Wrote:  Hi, I'm new here, since I'm looking for exactly this feature. Has anything changed since 2015? I'm presently streaming via MPD from an SOTM sms 200 ultra neo, which comes with the option of using minim-server. The music library is on a local NAS. Unfortunately, my DAC+Amp (Lyngdorf TDAI 2170) does not have a dedicated polarity switch, as do some other amps, and I'm looking for a software solution. (The Lyngdorf is capable of handling 32 bits at 384 MHz via USB.)

Apparently, Roon does have this feature, but first I would like to explore Minimserver/-streamer. The majority of material is encoded as FLAC, a few DSD-files are streamed via dop, as my DAC doesn't accept that format natively. If needed, Minimstreamer might be used to transcode to FLAC beforehand.

The option of switching polarity on the fly would help enormously in deciding which files are inverted, before fixing them offline, at least the FLAC-files

In order to offload the work from the SOTM sms 200, I could also try to move Minimserver and Minimstreamer to a dedicated Odroid N2.

-- Jürgen

P.S. In case you have difficulties hearing a difference when flipping the polarity, you may have 2-way or 3-way speakers, where the polarity is already flipped for some frequency ranges, but not for others.

You might like to try the following with Minimstreamer:-

stream.options
Code:
convOut=-af aeval=-val(ch):c=same

together with

stream.transcode
Code:
flac:wav;

For more detail refer to the ffmpeg filter aeval.

Basically, the negative (-) sign performs the reversal to all the channels. So, you could simply include/exclude this sign to compare the effect.
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05-01-2021, 22:19
Post: #6
RE: Polarity inversion
(05-01-2021 14:59)Alandbush Wrote:  You might like to try the following with Minimstreamer:-

stream.options
Code:
convOut=-af aeval=-val(ch):c=same

together with

stream.transcode
Code:
flac:wav;

For more detail refer to the ffmpeg filter aeval.

Basically, the negative (-) sign performs the reversal to all the channels. So, you could simply include/exclude this sign to compare the effect.

Thanks for the suggestion; I'm basically using this ffmpeg-command (or a similar one in sox) to flip the polarity. But will this work on the fly with minimstreamer? The whole point is to allow immediate comparisons between the two states to decide which one sounds better.

Presently I'm still fighting with tags. minimserver.log gives me a long list of things to fix, mostly dates...
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06-01-2021, 01:30 (This post was last modified: 06-01-2021 17:25 by Alandbush.)
Post: #7
RE: Polarity inversion
(05-01-2021 22:19)koslowj Wrote:  But will this work on the fly with minimstreamer? The whole point is to allow immediate comparisons between the two states to decide which one sounds better.

If I understand your question correctly, then Minimstreamer works in real time. It is not an offline transcode.
However, the transcode is for a complete track. You cannot change the transcode part way and expect the change to take place.
Also, the transcode is part of the track details sent to the control point/renderer. Replaying a track in a play queue will use the original transcode. The track must be removed from the queue and subsequently added to effect any transcode changes.

edit: just to clarify as per simoncn following post

"This is true for changes to stream.transcode but not for changes to stream.options (including convOut settings). Changes to stream.options are applied automatically when the next track is started."
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06-01-2021, 09:31
Post: #8
RE: Polarity inversion
I guess this rules out the solution proposed above. I want a software-simulation of a hardware button to flip polarity instantaneously. If this is impossible in software, I may have to consider building a box to be put between amp and speakers to accomplish this mechanically...
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06-01-2021, 10:23
Post: #9
RE: Polarity inversion
(06-01-2021 01:30)Alandbush Wrote:  Also, the transcode is part of the track details sent to the control point/renderer. Replaying a track in a play queue will use the original transcode. The track must be removed from the queue and subsequently added to effect any transcode changes.

This is true for changes to stream.transcode but not for changes to stream.options (including convOut settings). Changes to stream.options are applied automatically when the next track is started.
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06-01-2021, 17:27
Post: #10
RE: Polarity inversion
(06-01-2021 10:23)simoncn Wrote:  
(06-01-2021 01:30)Alandbush Wrote:  Also, the transcode is part of the track details sent to the control point/renderer. Replaying a track in a play queue will use the original transcode. The track must be removed from the queue and subsequently added to effect any transcode changes.

This is true for changes to stream.transcode but not for changes to stream.options (including convOut settings). Changes to stream.options are applied automatically when the next track is started.

My apologies for any confusion and thank you for the clarification.
Original post edited.
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