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Old 23rd May 2020, 07:35 PM   #971
Hensolo is online now Hensolo
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I noticed such a thing. In both ARTA and REW, when measuring the impulse response, the peak of the impulse is at the bottom. It is always necessary to mark “invert” so that the peak of the impulse is at the top. Why could this be?
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Old 23rd May 2020, 07:37 PM   #972
Pano is offline Pano  United States
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Because something in your signal chain is inverting the polarity. Perhaps your amplifier, your mic, your speakers?
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Old Yesterday, 11:57 AM   #973
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My signal circuit is computer> computer USB> external sound card> line-in output of the card> analogue input of the amplifier> amplifier> speaker. I checked the speaker and wires from the amplifier output - everything is correct. Maybe you have some files to check the polarity of the output of the amplifier and sound card?
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Old Yesterday, 12:06 PM   #974
jan.didden is offline jan.didden  Europe
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If you have a 2-channel scope or a 2-channel soundcard that can be used as a scope, measure the input signal with one channel, then go through your chain until you find the point where it is inverted. The cabling can be OK, but it's probably one of the parts of the chain.

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Old Yesterday, 12:31 PM   #975
Datsun is offline Datsun  Russian Federation
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Quote:
Originally Posted by Hensolo View Post
My signal circuit is computer> computer USB> external sound card> line-in output of the card> analogue input of the amplifier> amplifier> speaker. I checked the speaker and wires from the amplifier output - everything is correct. Maybe you have some files to check the polarity of the output of the amplifier and sound card?

The first peak may be negative when measuring multiband acoustics. This indicates that the tweeter is in antiphase to the woofer.


Also, the amplifier in its path can invert the signal in phase. This is checked simply: supplying a signal from the computer to the amplifier input. From the amplifier, the signal through the voltage divider goes to the input of the computer.
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Old Yesterday, 06:06 PM   #976
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I started the IR measurement from the sound card, the amplifier turned off. The polarity is upside down. So this makes a microphone or sound card. At the same time I found out that the amplifier is not necessary for measuring IR using REW. Sound card amplification is enough.
Now the question is, how to find out who inverts the polarity - a card or a microphone?
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Old Yesterday, 08:40 PM   #977
mbrennwa is online now mbrennwa  Switzerland
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Originally Posted by Hensolo View Post
Now the question is, how to find out who inverts the polarity - a card or a microphone?
Do two loopback measurements (soundcard output connected directly to soundcard input). One dual-channel measurement, one single channel measurement (DUT channel only, no compensation). The dual channel measurement should have normal polarity. If the single-channel measurement has negative polarity, you know it's not the microphone.
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Old Today, 12:13 AM   #978
DBMandrake is offline DBMandrake  Scotland
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Sorry if this has been asked before, but is there a way in Arta to do "deferred" impulse response measurement ?

By this I mean is there some way to export the test signal generated by the "Impulse response measurement" function (swept sine, periodic noise etc) as a WAV or FLAC file instead of being played back through the sound card ?

And then at a later time manually trigger an impulse record without simultaneously generating a new test signal ?

The use case for this is quite simple - I would like to be able to accurately measure the frequency response of DACs which cannot be connected to a PC running ARTA.

Such as the analogue output of an iPhone, the headphone output of a TV set, other music playing devices with their own inbuilt DACs etc.

These devices can play back WAV or FLAC files so could play back the test signal generated by ARTA if there were some way to export it.

Of course absolute phase information can't be obtained since the impulse gathering is not being performed in full duplex so there is no precise time control between when the test signal is played and capture is started, however a frequency response is all I'm looking for.

Is this possible in ARTA at the moment and if not would it be difficult to add something like this ?
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Last edited by DBMandrake; Today at 12:16 AM.
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Old Today, 04:02 AM   #979
Bob Richards is offline Bob Richards  United States
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Device under test
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Old Today, 11:48 AM   #980
DBMandrake is offline DBMandrake  Scotland
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Device under test
Could you be a bit more specific please ?
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