Absolute phase/checker found

I have a 2 different Wright Pre-amps and one reportedly maintains phase while the other does not. I have been wondering about this for years now and was searching for a way to test this. I found that the Google Play Store has a free app for this. I downloaded it and sure enough it works just as expected!
I had an old Android phone that I used for the input via the headphone jack as I don't have a long enough patch cord and read the results on the other android phone I currently use. There are good instructions with the download as well.

BTW, sure enough the WPL-20 maintains phase and the WLA-12A inverts phase. Interesting also that the transmission line port is out of phase just as the designer intended.

I don't know if the same app is available on IOS but for android users this is cool and free.
Just sharing a small success story.
 
Excellent point. Thanks so much!

Whether polarity is audible depends on whether all sounds that are heard have the same polarity. If they are all the same, no problem, but if some sound sources in the room are not of the same polarity, there can be big audible problems.

The ears aren't very sensitive to changes in polarity with almost all musical sounds. There are some artificial test signals that can facilitate the job of hearing changes in polarity.
 
My understanding is that some people can just about detect absolute phase on some programme material, and many programme sources do not preserve absolute phase. Thus for most people all of the time, and some people most of the time, absolute phase does not matter.

It is unclear to me how an 'app' (or anything else, apart from a Maxwell demon) can reliably determine absolute phase as it would have to know what the original music is.

The best way to tell if a preamp preserves phase is to study the circuit.
 

Pan

Member
2002-09-19 3:52 pm
The human ear can detect absolute polarity when using an asymmetric signal and the sensitivty is greatest in the 100Hz-500Hz or so and poor above a couple of kHz.

Flipping a random record on your system to find correct polarity is not clearing things up since nonlinear distortion in the speaker will interfer with this. In order to find out if you hear a polarity change and not different levels of distortion you need a very low distortion transducer.

Also phase shift (like from crossovers) can be audible.

Headphones and dry acoustics makes it easier to detect these things while in normal lively room, at some distance and with typical music material I think the conclusion is that we are not very sensitive and typically fail to detect phase changes that can be heard in a more controlled set up.

Sensitive or not, we can detect it in some situations.

You can make sure your stereo is correct polarity wise electrically, from source to amp output. It's harder acoustically since most speakers shift phase and have at least one driver connected with opposite polarity then the other driver(s).
 
My understanding is that some people can just about detect absolute phase on some programme material, and many programme sources do not preserve absolute phase. Thus for most people all of the time, and some people most of the time, absolute phase does not matter.

My experience is that then you ask those people to show you how they do it without non-audible cues and they become random guessers. I've seen it happen many times.

It is unclear to me how an 'app' (or anything else, apart from a Maxwell demon) can reliably determine absolute phase as it would have to know what the original music is.

It's painfully simple in a well-equipped shop. Just play an asymmetrical wave (most music and voice recordings are obviously so) and look at the input and output of the UUT with a 'scope.

The best way to tell if a preamp preserves phase is to study the circuit.

I don't know if its the best way, because often schematics are elusive. But if you have the schematic and know how to analyze circuits, yes its probably the easiest way.

Thing is, not all circuits are easy to analyze, and sometimes the circuit you want to analyze is not always exactly what the schematic seems to say. For example, there's a transformer in the circuit whose wiring is, ummm ambiguous.
 
Pan said:
Of course you can create and app that tells you the absolute polarity of a system. A known asymmetric signal is fed to the system and you record the output and check the result. Duh!
I assumed that the app can listen to music and determine the phase, or so it is claimed. Sending a signal in and looking at the output is trivial and not worth reporting, so I assumed that this app claims to do more than that. So is this thread about something which is trivial and blindingly obvious, or something that is impossible?
 

Pan

Member
2002-09-19 3:52 pm
My experience is that then you ask those people to show you how they do it without non-audible cues and they become random guessers. I've seen it happen many times.

This is something you can do 20/20 blind a bad day. Not with any material of course, but with a suitable signal.

In order to exclude distortion as a source of audible difference you need to measure the playback device and do a spectral analysis of the exact same signal and set up you will use for the blind test. It's hard to decide for a certain limit of the distortion components but they should be low, prefreably below hearing threshold, even though some masking will take place with most material.

Sawtooth at 50Hz - 500Hz is very easy to hear. Tympany and brass I've heard are some of the natural sounds that you can use as well (asymmetric signals as well).

It's funny to listen to sawtooth, flipping polarity makes it sounds like you changed frequency and also changed spectrum.