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Topic: Is there any software to analyze absolute polarity of an audio file? (Read 6105 times) previous topic - next topic
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Is there any software to analyze absolute polarity of an audio file?

Is there any (free) software that can reliably analyze the absolute polarity of an audio source, such as a WAV file? I've spent a frustrating few hours searching for a software method, with no success!

Win32 preferred for compatibility purposes, but willing to consider other options....

    - M.

Is there any software to analyze absolute polarity of an audio file?

Reply #1 –
Is there such a thing as absolute polarity? I can understand relative polarity, if two audio signals are identical except for a possible polarity inversion, but I have no idea what you could mean by absolute polarity.

Is there any software to analyze absolute polarity of an audio file?

Reply #2 –
Well absolute polarity is about which deflections from 0 are negative voltage, and which are positive. Which should translate into the membrane being pulled away from the listener and pushed towards them, respectively. Or vice versa, I don't remember what the standard is.

Any wave editor shows which deflectiona are negative, and which are postive - in digital domain. Preservation of absolute polarity depands of course on the entire signal chain, from the soudcard to the amp to the loudspeaker crossover.
Ceterum censeo, there should be an "%is_stop_after_current%".

Is there any software to analyze absolute polarity of an audio file?

Reply #3 –
Quote from: pawelq on
Well absolute polarity is about which deflections from 0 are negative voltage, and which are positive. Which should translate into the membrane being pulled away from the listener and pushed towards them, respectively. Or vice versa, I don't remember what the standard is.

OK, but how could you possibly deduce that from the contents of a wav file?

Is there any software to analyze absolute polarity of an audio file?

Reply #4 –
With PCM files alone it is impossible to reconstruct that without additional reference, for example a magnetic tape of the same recording.

If the file has a DC offset, that may provide a hint, though nothing conclusive.

Is there any software to analyze absolute polarity of an audio file?

Reply #6 –
I don't know of any such software.  If you were to write such a program, I think you'd get a probability of inverted or non-inverted phase, but I don't believe there is any way to know for sure.  As far as I know, most sounds don't even have a particular phase/polarity.  Exceptions might be kick drums & explosions.*

I found a waveform for a kickdrum (and a big discusson of polarity) on gearslutz.com[/u] (see post #44).

Personally, this isn't something I worry about:
1.  I've never heard any difference when inverting phase.
2.  There is no way of knowing if the phase was inverted during recording/production.
3.  I have no idea if my system maintains or inverts phase.



* Posts on gearslutz say that trumpts & trombones exhibit negative-going peaks.

Is there any software to analyze absolute polarity of an audio file?

Reply #7 –
Isolating a kick drum is an excellent idea.

Is there any software to analyze absolute polarity of an audio file?

Reply #8 –
Quote from: M on
Is there any (free) software that can reliably analyze the absolute polarity of an audio source, such as a WAV file? I've spent a frustrating few hours searching for a software method, with no success!

Win32 preferred for compatibility purposes, but willing to consider other options....

    - M.


Not sure if it has what you're looking for, but take a look at SoX:  http://sox.sourceforge.net/
Here's the manual: http://sox.sourceforge.net/sox.html

Is there any software to analyze absolute polarity of an audio file?

Reply #9 –
Quote from: rpp3po on
Isolating a kick drum is an excellent idea.



Even this has problems. It depends on which side of the drum the recording was made. If the microphone is placed in front of the drum, then we can expect an initial positive voltage, if however, the microphone was behind the drum, then we can expect an initial negative voltage. All this is assume everything else in the signal chain maintains correct polarity.

Is there any software to analyze absolute polarity of an audio file?

Reply #10 –
Quote from: Iain on
Even this has problems. It depends on which side of the drum the recording was made. If the microphone is placed in front of the drum, then we can expect an initial positive voltage, if however, the microphone was behind the drum, then we can expect an initial negative voltage. All this is assume everything else in the signal chain maintains correct polarity.

A kick drum will hardly be mic'd from behind, since that would pick up noise from the pedal. Microphone placement would be somewhat difficult too.

Is there any software to analyze absolute polarity of an audio file?

Reply #11 –
Quote from: gaekwad2 on
Quote from: Iain on
Even this has problems. It depends on which side of the drum the recording was made. If the microphone is placed in front of the drum, then we can expect an initial positive voltage, if however, the microphone was behind the drum, then we can expect an initial negative voltage. All this is assume everything else in the signal chain maintains correct polarity.

A kick drum will hardly be mic'd from behind, since that would pick up noise from the pedal. Microphone placement would be somewhat difficult too.


Granted, it is unusual. I have, however, mic'd the whole kit with a stereo pair behind the drummer's head, and in desperate situations one mic carefully placed below the snare will double as a kick mic and a snare mic.

My point is that it is impossible to be certain about the 'absolute polarity' of a recording.

Is there any software to analyze absolute polarity of an audio file?

Reply #12 –
Quote from: pdq on
OK, but how could you possibly deduce that from the contents of a wav file?


Well sample values in a 16-bit wave file range from -32768 to 32767. I'd assume that in a proper DAC negative sample values translate to negative voltages and postive sample values translate into postive voltages, in the range ~-5V...+5V. Or are you just saying that one can't tell if somewhere in the path from the microphone to the digital file polarity was not reversed?
Ceterum censeo, there should be an "%is_stop_after_current%".

Is there any software to analyze absolute polarity of an audio file?

Reply #13 –
I think the short answer here is that any application that displays a waveform can display its polarity (positive vs. negative sample values).  Audacity comes to mind as free and capable, I'm certain there are others too.

http://audacity.sourceforge.net/

However, given that the entire recording chain, differences in the original signal source (acoustic, electronic, etc.) and unpredictability of the recording and playback process would make it difficult to say what the "correct" polarity would/should/could be.  Even individual instruments in the recording could be mixed in with different relative polarities.

So, I'd say install Audacity or another program and have at the waveform analysis.
Was that a 1 or a 0?