I think I understand how to create an impulse response with my hardware gear, but how can I use an impulse response to negate the effects of a piece of gear?
Let's say I record a chain consisting of a nice amp, a nice mic, and a cheap, poor-quality preamp. Let's say the preamp is overly-bright. So, before perhaps applying another mic pre impulse response, I want to "correct" the overly-bright sound bringing it closer to an accurate neutral one. Can I create an impulse response of the pre and then "flip" or "reverse" it so that it lessens the coloration of the too-bright pre? If so how?
Creating a "Regularization" impulse response?
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- KVRian
- 1272 posts since 11 Apr, 2002 from Nashville, TN
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- KVRian
- 1379 posts since 26 Apr, 2004 from UK
First, you need to know that you will only be able to remove the linear transformation. If your gear creates harmonics, it's over, you can't.
Now, to create a reverse impulse, you need a high end sound card (last time I was on such a project, only Metric Halo could deliver the precision in time required, not even RME, but that was 10 years ago). It's not a matter of low noise, it's a matter of I/O synchronization and precision.
Then create a Hadamard transform of sufficient length (i.e. more than your final impulse) and drive it inside your gear and record the result. Once you have several times your Hadamard length, apply the inverse transform on e 2 to last impulse and average them.
You know have the impulse of your gear. You need to deconvolve your original signal with this impulse (there are deconvolvers that exist as plugins).
Why a Hadamard transform instead of a pulse? A proper pulse is difficult to achieve (more than a Hadamard transform signal), and the Hadamard inverse transfor is "quite" easy. And even a proper Hadamard transform is difficult for the majority of the sound cards.
Now, to create a reverse impulse, you need a high end sound card (last time I was on such a project, only Metric Halo could deliver the precision in time required, not even RME, but that was 10 years ago). It's not a matter of low noise, it's a matter of I/O synchronization and precision.
Then create a Hadamard transform of sufficient length (i.e. more than your final impulse) and drive it inside your gear and record the result. Once you have several times your Hadamard length, apply the inverse transform on e 2 to last impulse and average them.
You know have the impulse of your gear. You need to deconvolve your original signal with this impulse (there are deconvolvers that exist as plugins).
Why a Hadamard transform instead of a pulse? A proper pulse is difficult to achieve (more than a Hadamard transform signal), and the Hadamard inverse transfor is "quite" easy. And even a proper Hadamard transform is difficult for the majority of the sound cards.
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- KVRian
- Topic Starter
- 1272 posts since 11 Apr, 2002 from Nashville, TN
Would the character of a mic pre typically be determined by harmonics or linear qualities? I am not at the tech level of your initial answer.
What I am really trying to do is to be able to bend my mixers pres to the sound of my three outboard neve flavored SCA N72 pres. My mixer is pretty clean, but I wanted to first clear the slate, so to speak, and then apply the impulse of the neve pres to all tracks coming in from the board.
Which devolver do you recommend?
What I am really trying to do is to be able to bend my mixers pres to the sound of my three outboard neve flavored SCA N72 pres. My mixer is pretty clean, but I wanted to first clear the slate, so to speak, and then apply the impulse of the neve pres to all tracks coming in from the board.
Which devolver do you recommend?
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- KVRian
- 1379 posts since 26 Apr, 2004 from UK
It's probably the harmonics...
I don't have a deconvolver to propose, I would implement a filter myself in Audio ToolKit for this purpose.
I don't have a deconvolver to propose, I would implement a filter myself in Audio ToolKit for this purpose.
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- KVRist
- 288 posts since 3 Mar, 2004 from Denmark
Weeeeeeelllllllll.... it's not very practical, but you canMiles1981 wrote:First, you need to know that you will only be able to remove the linear transformation. If your gear creates harmonics, it's over, you can't.
http://home.deib.polimi.it/sarti/August ... redist.pdf
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- KVRian
- 1379 posts since 26 Apr, 2004 from UK
Not with a linear process, the OP wanted to have an impulse, which by definition is a linear process that cannot create harmonics.