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Author Topic: speakers out of phase?  (Read 15503 times)

speculatrix

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speakers out of phase?
« on: June 20, 2018, 06:29:46 am »
i was watching a youtube video and I was enjoying the stereo sound when I realised the sound seemed odd, there was no central stereo image. I think it's because the speakers are mis-wired and thus out of phase.

Just me?

Or is it some sort of audio processing that's meant to give a faux wide field effect?

I'm wondering if there's an audio player for android which allows reversing the phase of one channel so I can do a test to try and prove I am right.
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Gemini 4G/Wi-Fi owner, formerly zaurus C3100 and 860 owner; also owner of an HTC Doubleshot, a Zaurus-like phone.

drand

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speakers out of phase?
« Reply #1 on: June 20, 2018, 08:33:19 am »
I know there are apps such as Polarity Checker that allows you to check a speaker for this by playing a series of test audio files. Perhaps if you have another android device you could use it to check the Gemini. I might give it a go later if I can.

I know that my ears can't detect phase difference but I do think the Gemini's sound quality is poor having watched a few vidoes.
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speculatrix

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speakers out of phase?
« Reply #2 on: June 20, 2018, 12:57:34 pm »
I tried this app and it reported nine out of ten times, if not more, that my speakers are out of phase.
https://play.google.com/store/apps/details?...polaritychecker
« Last Edit: June 20, 2018, 12:57:45 pm by speculatrix »
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speculatrix

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speakers out of phase?
« Reply #3 on: June 20, 2018, 01:25:57 pm »
I installed a tone generator and playing a tone give me a central image using bluetooth or wired headphones but not with speakers.

https://play.google.com/store/apps/details?id=com.xyz.signal

warning: turn volume right down before turning on the sound, and raise volume slowly, then lower it before switching to headphones!
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speculatrix

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speakers out of phase?
« Reply #4 on: June 20, 2018, 05:14:21 pm »
Quote from: drand
I know that my ears can't detect phase difference but I do think the Gemini's sound quality is poor having watched a few vidoes.

human ears are relatively insensitive to phase, but when the signal from stereo speakers is totally out of phase you'll know.
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iusethis

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speakers out of phase?
« Reply #5 on: June 20, 2018, 06:18:49 pm »
Planet have mentioned that the speakers are currently mono only, but this will be fixed in a future firmware update. That said, it sounds like the polarity on one of the speakers is inverted or else something funky is going on there, so not sure if that can be fixed in software.
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TallTim

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speakers out of phase?
« Reply #6 on: June 20, 2018, 07:15:32 pm »
Quote from: iusethis
Planet have mentioned that the speakers are currently mono only, but this will be fixed in a future firmware update. That said, it sounds like the polarity on one of the speakers is inverted or else something funky is going on there, so not sure if that can be fixed in software.

I wonder if anyone has noticed lower volume through headphones? I don't get the warning like you would in other devices in Android for raising the volume through settings -- but I do wonder if there is some kind of limiter on the top-end volume level.

This is going through some pretty high-quality headphones too, so it wasn't a factor of crap connection or gear.
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speculatrix

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speakers out of phase?
« Reply #7 on: June 21, 2018, 03:05:52 am »
ah, I didn't realise the speakers were mono.
in that case, the sound should appear to come from the centre all the time with no sound stage.
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zevv

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speakers out of phase?
« Reply #8 on: June 21, 2018, 11:53:11 am »
I noticed the same thing, it's quite annoying really. I made some measurements the other day, here's a recording of a 440Hz sine wave with two
mics on each speaker:

https://i.imgur.com/dfWhKl6.png

I really do hope planet will fix this on the short term, it makes playing any kind of audio a nuisance.


----
edited by admin, re-uploaded image to imgur so that it can have an https URL and thus show correctly in the forum. ~speculatrix
Varti: image link is now broken, couldn't find it on archive.org as well :(
« Last Edit: September 15, 2020, 05:56:56 am by Varti »
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zevv

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speakers out of phase?
« Reply #9 on: July 17, 2018, 12:20:15 pm »
After some hacking in the audio drivers I am now able to fix the speaker phase with a rather nasty but functional kernel hack that simply inverts the polarity of one channel of the audio data before it is sent to the codec. It is rather incredible how much better the sound is with the phase fixed, not only does the sound not originate from behind your eyes anymore, but there sound is much fuller with more low in it.

The problem I now run in to is that the phase is reversed with using headphones, as the same codec path is used for both headphones and speakers, so I will need to find some kind of detect if the headphones are active and only reverse phase if this is not the case.

I might also be able to fix the crackle-when-nothing-is-playing issue while I'm at it by not powering down the I2S path when audio playing is paused, but that might have implications on power usage, of course.

For the brave of heart, here is my android kernel boot image with the phase fixed: http://zevv.nl/div/linux_boot-phasefix.img. (No, I take no responsibility for any bricking or other harm done to your device!)
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jakfish

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speakers out of phase?
« Reply #10 on: July 17, 2018, 12:58:39 pm »
Well, hats off to you. Amazing! Have you explored your work with Planet? You seem to be on to something and they should know about it.

Jake
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speculatrix

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speakers out of phase?
« Reply #11 on: July 17, 2018, 03:53:33 pm »
wow, zevv, that's awesome
I had been thinking of trying to pop open the G's case and swapping the wires round on one of the speakers.
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Kiriririn

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speakers out of phase?
« Reply #12 on: July 17, 2018, 07:49:30 pm »
Quote from: zevv
After some hacking in the audio drivers I am now able to fix the speaker phase with a rather nasty but functional kernel hack that simply inverts the polarity of one channel of the audio data before it is sent to the codec. It is rather incredible how much better the sound is with the phase fixed, not only does the sound not originate from behind your eyes anymore, but there sound is much fuller with more low in it.

The problem I now run in to is that the phase is reversed with using headphones, as the same codec path is used for both headphones and speakers, so I will need to find some kind of detect if the headphones are active and only reverse phase if this is not the case.

I might also be able to fix the crackle-when-nothing-is-playing issue while I'm at it by not powering down the I2S path when audio playing is paused, but that might have implications on power usage, of course.

For the brave of heart, here is my android kernel boot image with the phase fixed: http://zevv.nl/div/linux_boot-phasefix.img. (No, I take no responsibility for any bricking or other harm done to your device!)

Awesome find! Can you share the source code of your change?
« Last Edit: July 17, 2018, 07:49:47 pm by Kiriririn »
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zevv

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speakers out of phase?
« Reply #13 on: July 18, 2018, 03:47:34 am »
Quote from: Kiriririn
Awesome find! Can you share the source code of your change?

https://github.com/zevv/gemini-android-kern...7a00d2dfb7af32c
« Last Edit: July 20, 2018, 04:29:12 am by zevv »
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Anonymous_

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speakers out of phase?
« Reply #14 on: July 19, 2018, 04:48:12 am »
zevv: does this mean L and R channels get separated with your fix? As before L channel has been played in both speakers as well as R channel.
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