Impulse response is inverted

[Lesmor]

A friend of mine sent me his mdata and I noticed the impulse response of all his speakers is inverted
it is the first time I have come acreoos this
can anyone explain why this happened

 

[John Mulcahy]

Inversions can happen anywhere in the chain, perhaps more commonly in the audio interface.

 

[Lesmor]

Inversions can happen anywhere in the chain, perhaps more commonly in the audio interface.

Thanks John
I would like to see if he can rectify this
can you expand a bit regarding where in the audio interface
Andy

 

[John Mulcahy]

Some audio interfaces invert their inputs, some invert their outputs, some have buttons to invert which may get pressed inadvertently. Some processors and some amplifiers invert their outputs. If the measurements were made with a USB mic the inversion is probably in the output path somewhere, I haven't come across any USB mics that invert.

 

[Lesmor]

Thanks John mutch obliged
he used a UMIC 1 we will need to investigate further

 

[John Mulcahy]

Make sure Invert is not selected on the Input options of his REW soundcard preferences, and Invert impulse is not selected in the impulse graph controls.

 

[Lesmor]

Having he checked none of the settings were inverted
I suppose a obvious question should be does it matter if the impulse is inverted?
and if so why?

 

[sm52]

In my experience, many condenser mics invert, dynamic ones don't. Also a microphone preamp can do this. Or a setting in the sound card control panel. REW has an invert button, it's on the SPL tab and on the Impulse tab. So you can click it. But always remember that it is pressed. In order not to think about it, you need to find the culprit. and deal with it. Positive or negative polarity matters, but not in all cases. For example, you want to find out the polarity of drivers in speakers. Or set them to the polarity you need. Also, the type of phase characteristic changes from a change in polarity.

 

[Lesmor]

In my experience, many condenser mics invert, dynamic ones don't. Also a microphone preamp can do this. Or a setting in the sound card control panel. REW has an invert button, it's on the SPL tab and on the Impulse tab. So you can click it. But always remember that it is pressed. In order not to think about it, you need to find the culprit. and deal with it. Positive or negative polarity matters, but not in all cases. For example, you want to find out the polarity of drivers in speakers. Or set them to the polarity you need. Also, the type of phase characteristic changes from a change in polarity.

Thanks for the reply and your thoughts

1. as posted he is using a UMIC 1 so I think we can discount the mic
2.I find it inconcevable that he has the whole system wiring crossed, but I did reluctantly suggest this and he confirmed no issue
3. he has a couple of historic mdat files albeit at that time it was a different system and the impulse graphs on them were correct

this system consists of JBL Syntesis SCL2 L/C/R SCL4 surrounds
a Trinnov Altitude 16 with ATI power amps nothing obviously wrong

so I think that just leaves the laptop soundcard but as stated with his historic mdat files that didnt seem to be a issue

Is there an easy way to determin if a laptop soundcard inverts the signal?

 

[sm52]

2.I find it inconcevable that he has the whole system wiring crossed, but I did reluctantly suggest this and he confirmed no issue

This is the very first thought when an adult is engaged in the matter of measurements. But. For two weeks I was next to a person who understands electrical circuits, solders himself, creates devices for sound reproduction. I understood that something was wrong in the sound, but I could not say that he mixed up the wires. It turned out to be just that. He messed up the wires.

To find out who is to blame, the easiest way is to change one device for another at a time, one sound card for another, for example. One pair of wires to another. To see what will change.

 

[perceval]

I had the same inverted impulse once, and was baffled as I was sure the wiring was done properly, the mic was fine, having been used before.
The only thing that had changed was the amp... and I found out that the new amp was internally wired inverted!
Black was positive and red was negative.

Hiccup at the factory, I guess.

So, I have been inverting the wiring on that amp since.

Maybe your friend can check the polarity of the output from the amp. Stuff happens....

 

[Lesmor]

I had the same inverted impulse once, and was baffled as I was sure the wiring was done properly, the mic was fine, having been used before.
The only thing that had changed was the amp... and I found out that the new amp was internally wired inverted!
Black was positive and red was negative.

Hiccup at the factory, I guess.

So, I have been inverting the wiring on that amp since.

Maybe your friend can check the polarity of the output from the amp. Stuff happens....

thanks for the feedback
He used to have a Emotiva and I belive the XLR on that amp is inverted
the ATI should be good

 

[linearphase]

A friend of mine sent me his mdata and I noticed the impulse response of all his speakers is inverted
it is the first time I have come acreoos this
can anyone explain why this happened

View attachment 57428

It really doesn’t matter as long as both speakers are the same. If it really bothers you just select invert in the gears menu dialog.
Just curious why do you have the graph so compressed horizontally? That is not a very useful display for anything I am aware of.

 

[Lesmor]

It really doesn’t matter as long as both speakers are the same. If it really bothers you just select invert in the gears menu dialog.
Just curious why do you have the graph so compressed horizontally? That is not a very useful display for anything I am aware of.

over the years I have seen hundreds of REW files and this is the first time I have seen a inverted impulse
that said if it doesnt matter then we can move on

As for the graph, it is only to demonstrate the inversion

 

[perceval]

It will matter only if you try to blend other speakers with them, like a sub(s) or surrounds.
He will have to either invert polarity on his speakers, or on the sub(s) and surrounds.