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Old 7th May 2010, 12:33 PM   #1
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Default Inverse RIAA signal generator

Is there a signal generator that incorporates an inverse RIAA circuit available in the market? I don't want to use an external Inverse RIAA circuit because it may be incorrect (and difficult to calibrate) and induces hum.
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Old 7th May 2010, 12:50 PM   #2
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I've never seen such a thing, but my experience is that inverse networks have to be physically placed right at the preamp input, and often a heavy ground strap run to the chassis, otherwise the hum levels will contaminate distortion measurements. RIAA compensation in the signal generator might not be useful and it probably wouldn't be as accurate as what you can build yourself.

Conrad
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Old 7th May 2010, 03:27 PM   #3
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If you are using a data acquisition card, you can use the polynomials for the correct time constants to just massage the data in situ.

Numerator: 1 + X* 3.255e-3 + X^2 * 2.385e-7
Denominator: 1 + X*318e-4 + X^2 * 1e-12

I wrote a program for my HP3577a network analyzer to do this via the GPIB, (can't find the program) you should be able to do it with a sound card -- if the data on the sound card is valid to >50kHz.
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Old 7th May 2010, 03:34 PM   #4
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I have a 24/96 inverse riaa wav file with 100 10th octave tones placed at exact bins for a 64k FFT. The phase is randomized so it is psuedo-random. Better than .0005dB, I've been using it to verify biquad digital RIAA filters.
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Last edited by scott wurcer; 7th May 2010 at 03:37 PM.
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Old 7th May 2010, 03:39 PM   #5
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Quote:
Originally Posted by Sunsun22 View Post
Is there a signal generator that incorporates an inverse RIAA circuit available in the market?
Audio Precision has it.

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Old 7th May 2010, 05:30 PM   #6
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Quote:
Originally Posted by Nelson Pass View Post
Audio Precision has it.

I figured he might want something cheaper. It is amazing, rippling only a four coefficient IIR filter through an unequalized file is better than .00057dB and +-2 degrees from minimum phase and perfect channel to channel match. Better than any set of R's and C's. No noise or distortion either.
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Old 7th May 2010, 05:34 PM   #7
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There is this: Hagerman Technology LLC: iRIAA Filter for Phonostage DIY Kit
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Old 7th May 2010, 05:48 PM   #8
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You could put a standard or computer function generator into this:
Reverse RIAA Equaliser
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Old 7th May 2010, 06:12 PM   #9
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Here is an article with a simple inverse RIAA network. http://waltjung.org/PDFs/A_High_Accu...AA_Network.pdf

Ray
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Old 7th May 2010, 08:40 PM   #10
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Many thanks for the input.
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