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Old 27th September 2003, 01:57 PM   #11
tmd1 is offline tmd1  Ireland
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John,
I can't wait to hear these amps myself. I bought kits from the US as I don't have the wherewithall to design them myself. The reviews I have read were great.
As for the vinyl project, I have read of guys doing it before. You might take a look at www.audiocircle.com or www.harmonicdiscord.com and do a search. I remember one guy who was tickled with the results of his efforts.
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Old 27th September 2003, 06:48 PM   #12
jkeny is offline jkeny  Ireland
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Default RIAA correction digital filters

Does anybody know of examples of dig filters to do RIAA (phono) correction using possibly Cooledit or similar to convolve? Also what about using a filter to correct for cartridge anomalies?

I'm thinking along the lines of getting a test signal vinyl disk. Recording a sweep signal into spectrum analyser software and using the difference between this recorded signal and true signal as a correction to tracks recorded from my cartridge/TT combo

Strikes me this method would give pretty excellent vinyl playback without the expense of high end equipment.

Neil, BTW, there is a shop on Aungier called Back to the Future which has CUBIT silent PCs for sale - these are Pentium 4 PC with 4 USB 2 Firewire 1PCI 1 AGP etc and pretty silent fans - reviewd in this months PCPro and got an A list rating I think.

Matt, I'm going to look up your USB reference but do you have any site refs which have done this?

John
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Old 27th September 2003, 07:32 PM   #13
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Hi,

I am using an M-Audio Audiophile 2496 PCI soundcard and this one sounds really good. It has also some good options for modding. You can address the M-Audio drivers directly from your software. No need for the Windows mixer, although you can use it. This card is very silent with very low PC related spurs. At the moment it is part of my audio test bench with FFT software.

But I have found that with an on-board soundcard the main board is also important. At the moment I am using an MSI main board and this is far more silent (at the output of the soundcard) than my previous Abit main board.

Cheers
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Old 27th September 2003, 07:35 PM   #14
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Be careful when doing EQ or RIAA correction in the digital domain. You can't have gain in the digital domain without clipping a 0db signal... so you are basically always attenuating it.

Attenuation in the digital domain loses dynamic range unless you first convert all values to floating-point, do the calculation, and then dither them down to 24 bit and use a 24bit DAC.

Still, in any frequency range where you have more than 24db attenuation you will be losing information.
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Old 27th September 2003, 07:35 PM   #15
tmd1 is offline tmd1  Ireland
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Thanks John, I may check them out.

Pjotr,
Are you using that sound card for digital or analogue out?
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Old 28th September 2003, 10:30 AM   #16
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Hi TMD and others,

I am using the analog outputs. It is important to keep the audio interlinks away from the mains cord and other digital links. There is otherwise more noise coupled into the interlinks than induced by the computer itself. Iíve modded the card a little bit by putting extra R-C filters in the +12V and Ė12V power lines. This dropped noise some 10 dB. The codec chips are from AKM. These chips are voltage out and can drive directly 600 ohms. So there is the option for a passive low pass filter and line transformer output. There is a clock generator onboard that is set to the real sampling rate as dictated by the .wav files, no re-sampling at all. This clock generator is open for modding to an ultra low jitter one.

I am for sure not saying that this is the best solution. But concerning noise and jitter there is absolutely no need to go for an outboard (USB) card. The M-Audio card has S/PDIF out, so you can hook up your top-gear external audiophile DAC with extensive extra PLL jitter reduction.

On the other hand the audio data is usually buffered and synchronised to the X-Tal clock on a good soundcard. This also holds for USB cards. So jitter can be minimised to the max without PLLís

-------------------------------------

BTW, is there anyone out there who knows of good playback software that reads a complete CD (stored on the hard disk) or a set number of .wav files in RAM memory, stops the hard disk and starts playing the music from memory?


Cheers
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Old 29th September 2003, 10:12 PM   #17
tmd1 is offline tmd1  Ireland
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Pjotr,
I was thinking along the lines of an outboard DAC for other reasons than noise. It would help for it to remain more flexible to use different sources and DACs for one.
Is there a way of getting I2S off a computer somehow? Does a soundcard generate this? From my very limited understanding of it, wouldn't it be better as output than S/PDIF?
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