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Old 20th January 2005, 01:40 AM   #1
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Default RIAA preamp curve page?

there was a website that showed how to duplicate the RIAA EQ curve on the PC.

If memory serves, this was part of a method of bypassing the RIAA preamp alltoghether by inputting the turn table directly into a soundcard and creating the EQ in a WAV editor.

Anyone know what I am talking about?

My HD was corrupted late last year and I lost all that info and all my bookmarks.


Darren
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Old 20th January 2005, 03:55 AM   #2
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The RIAA playback curve varies by almost 40db from 20Hz to 20kHz, 20dB boost at 20Hz and 20dB cut at 20kHz referenced to 1kHz. A typical moving magnet phono cartridge has 3mV output, 30mV output at very most.

I assume you want to use the soundcard mic input which probably has enough gain, then EQ in software for increasing gain with decreasing frequency. I guess it would work if you could tolerate losing 7 bits of resolution, or in other words for 60dB S/N at 20Hz or 80dB at 1kHz after EQ you would need 100dB S/N before EQ, referenced to 3mV at 1kHz. Doing this with a high performance 24-bit sound card with a good mic preamp should be better than using a low performance phono preamp, but probably not as good as using a good phono preamp with its RIAA EQ.

If you google on "RIAA curve" or "RIAA equalization" you should find the info you are looking for.
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Old 20th January 2005, 07:47 AM   #3
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Implementing a correct RIAA in the 44.1k sampled domain and using commercial WAV editors is probably bound to fail or else fiendishly complex to get right.

The analogue-domain RIAA transfer curve can not be directly mapped into the Z-domain as in the latter 'infinity' happens at 22.05kHz,
and the resulting filter needs to be dewarped seriously to attain a correct response at 20kHz. Not even mentioning correct phase behaviour.

Doing it in 88.2k or 96k will be somewhat easier.


BTW, outfits like TerraTec offer 'RIAA compatibility' of some of their soundcards in exactly the way you describe: a high-gain flat input amplifier, then ADC, then a software part that de-RIAAs the wav file. Hardly good practice, but then what do you expect from TerraTec?
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Old 20th January 2005, 07:54 PM   #4
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Audacity has an riaa filter and some for 78rpm defined already.
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