[Syrah]

I just read Michael Fremer's review of the Channel D Pure Vinyl program for Macs.  It is for digitizing vinyl, but it uses the computer to apply the RIAA equalization curve in the digital domain, rather than a phono stage.  One uses a Mic amp to apply the gain from the cartridge.

It got me thinking.  What if one plugged an MC cartridge into a high quality Mic amp and fed a DBX Driverack or Behringer, then you could use the digital EQ to apply the RIAA curve yourself while compensating for room acoustics at the same time?  Then plug the DBX or Behringer out into the line level preamp.

I know the purists will say that you cut out the vinyl benefits by subjecting it to AD/DA conversion.  But you also avoid the analogue circuitry used to shape the RIAA curve, you convert at high resolution, and you get room EQ at the same time.

Any thoughts?

[analognut]

You can't use a hardware eq to get your RIAA curve. The low end of the curve requires vastly more gain than a hardware eq is able to apply. You need a software eq like the Waves Q10 where you can apply up to 18db of gain on a single band, then stack the next band on top of the first and apply 18db more gain, etc. I have the Behringer 24bit Dual DSP (dual mono) 31-band hardware eq and would never consider it for that use.

Even if you could get the gain out of a hardware eq, you would be attempting something the hardware isn't designed for and would be introducing all kinds of nasty problems into your low-output phono signal! You want to keep that low-output MC signal as pure as possible, at least until it gets fully amplified!

I don't know what your goal is. If your goal is room eq, do it after the preamp!! If your goal is to make computer recordings of your LPs, and you want to do the RIAA in the computer, use a good software eq like the Waves Q10. Waves claims the Q10 is the world's most powerful eq, and it is fully phase-compensated, as is all their software. The Waves software is IMHO the finest audio production software available anywhere in the world, at any price. I own the Q10 and much more of the Waves software and speak from personal experience.

I would recommend against using a flat-response preamp at all. I have one and for years it's what I used, in conjunction with the Q10. I'm saying if you have the hardware, don't use it, and if you need to buy the hardware most certainly don't waste your time! Spend your money on upgrading the vinyl front-end. And even a $150 phono preamp will have specs stating the RIAA curve is accurate to +/- 0.5db! Case in point: Hagerman Bugle. It's very difficult to draw a curve that's any more accurate than that, even using the Q10.

Another big disadvantage to doing RIAA in the computer is that you can't listen properly to the music as it's being recorded. I now use a traditional phono preamp and listen to everything as it's being recorded. That way if I hear a loud pop which I feel my software won't take out properly I can place a marker in the recording and go in later and manually remove it. The result? I end up with better-sounding CDs, of course!  ....

Cheers, and happy listening!
John

[Syrah]

Thanks for this John.  Have you compared the sound using the Q10 for RIAA eq vs. using your phono stage for RIAA eq?  For example, doing two recording of the same LP, one going via phono stage (then to Q10) and the other with a mic amp (then to Q10)?

Either way, I will definitely check out the Q10.

Cheers.

[analognut]

Syrah,

If you are recording through a flat-response preamp and applying a standard RIAA eq curve in your computer, then the sound will be slightly different (to my ears better) than recording the sound from the low-output MC run through the standard phono stage. But for the better sound you need to use the best software available in a 32bit Floating Point environment. I don't know what you're using, but a $50 editor will not do this.

The reason for the better sound is that most low-output MC have a peak in the frequency response at the high end and you are automatically correcting this when you adjust your software eq to apply a perfect RIAA curve, which I think is way cool, and you're automatically eliminating any other frequency deviations from the RIAA which may be introduced through your TT and cart setup. You would also be changing the signal to be absolutely flat all the way down to 20Hz, which is cool, but in the real world not necessary at all, since many recordings are rolled off during the mastering process at anywhere from 50-75Hz!

But you're still better off doing the RIAA with your phono preamp. For instance, if you make any adjustment to your TT which changes the sound even slightly, such as height of the tonearm, tracking force, damping of the arm, etc, you are then required to change your RIAA eq curve in the computer, and it turns into a big can of worms. You end up spending all your time recording the pink-noise track off your test record through the flat-response preamp so you can get your RIAA curve right again, and it's not worth all the time spent doing that. It ends up being a whole lot easier to just play the record with a normal phono preamp where you can listen to the sound as it's being recorded, and do the eq later, or not. My approach now has been to upgrade my vinyl front-end and make sure it's set up correctly. Then, if I'm not liking the sound of an LP I "tune it" by varying the cart load, VTA, VTF, and damping. But ultimately the idea is to find the combination which sounds right on (almost!) every LP. Then you know you've got it right, and you can spend your time making music and not fiddling!

When I was "into" doing the RIAA in the computer I tried plug-ins from all the manufacturers in my audio editor and the Waves software stood out as being ultra-transparent, very sweet-sounding, and without a doubt the best-sounding software I had ever gotten my hands on. I purchased enough of it as individual stand-alone plug-ins so that every single calculation that my computer makes is now done using a Waves plug-in.

Are you making CDs from LPs? If so, my recommendation is just use a regular phono preamp. Take the money you would have spent on the Q10 and apply that towards getting the Waves Restoration Bundle. Everything they sell is available free to try for 2 weeks, but buy from a pro-audio dealer at reduced cost.   

[doctorcilantro]

Starting from the principle that you don't really need 47K for a moving iron or moving magnet, 1K will do (I use 18K), this opens up MANY possibilities. VERY high quality mic preamps can then be used which have specs that are found in very expensive phono stages.

Have had this archived in my email for some time from AA:

"As the load impedance approaches the DC resistance of the cartirdge the damping effect is much greater for a slight reduction in impedance but as you go the other direction the source impedance is so low, relatively speaking and inthis case less than 40 ohms, the ratio of source to load is already very small at 1000 ohms and is reaching the point of diminishing returns. an incease to 5K or 47k doesn't do much. 47K was a convenient value but 1K would have been just as good for most MMs. "

You don't want to do any gain, if possible, in software, then you are working (i.e. digital RIAA and noise reduction) in the low end of 32bits. Common knowledge as AnalogNut stated, but there are ribbon mic preamps out there with incredible neutrality and tons of gain. So the gear is used for said purpose, it's out there at various price points and the impedance on many will work if you have something with low relatively low internal impedance like a Grado (Reference Statement has 2ohm).

I have found the AEA TRP to be ideal for digital RIAA implementation. Using MG-1 tonearm and Grado Reference Statement (.5mv) I do about 70db with the AEA. I was using a Lavry DA-10 but have settled on just using the sound card (1616M); the front end is probably more important here.

On Windows, you'll need something like Samplitude (or any VST capable app) and run the IEEQ plug-in from Jiittee at head-fi which he claims (and shows some math) is as good as Orban's PurVinyl filter which is VERY good.

I run realtime 32/96 recording and monitoring (simultaneous) with a touch of Algorithmix noise reduction. You can add butterworth etc with other plugs.

Some of the software I have noted is not cheap but if you search Head-Fi you'll find a completely free implementation using Max. You just need to get some decent hardware. The ART Gold mic preamps (tube hybrid) offer a ton of gain and also have the exact same ADC chip that is in the dedicated EMU 1212/1616 sound cards.

Lots of fun and sounds great!

DC

[doctorcilantro]

Oh, and Analognut I think I remember some folks trying to run MCs (or Grado's MIs) at 1K - 10K to try to heal that high frequency ringing; have you heard about that before. I need to set my system back up but it sounded damn good to me.

Also, I'm not quite sure about

"But you're still better off doing the RIAA with your phono preamp. For instance, if you make any adjustment to your TT which changes the sound even slightly, such as height of the tonearm, tracking force, damping of the arm, etc, you are then required to change your RIAA eq curve in the computer, and it turns into a big can of worms."

We don't do this with analog stages why would it suddenly change in the digital realm? You can't adjust the RIAA curve of your analog stage, you adjust mechanical parameters, as you said VTA, VTF, etc.

Same holds true in the digital realm, you can however choose some various curves using DiamondCut which is handy, depending on the cut/date of the vinyl.
DC

[analognut]

You don't want to do any gain, if possible, in software

Doctorcilantro-
I'd like to first comment on the above quote:
You will most likely be using 32bit Float in your editing. In this environment you can make as many gain changes as you like. It does not change any samples, only a mathematical relationship. If you have recorded with most peaks falling around -6db changing the level in the computer won't make 2 cents worth of difference in the noise floor. The normal procedure would then be to normalize against peak in the computer or if you limit a few peaks as I do, using the Waves L1 Ultra-Maximizer, normalize to some rms value.

You mention recording at 32/96 and realtime monitoring. What soundcard are you using? That's impressive- most soundcards won't record in 32bits. Personally, I don't need to go that high. Recording at 24/88 and processing in a 32bitFP environment is plenty of resolution for making CDs from my LPs. Any more and IMHO it just wastes processing power, and of course makes gigantic files. You must have a really big computer if you're recording flat and doing the RIAA eq in the computer and listening to the output at the same time! Or did I misinterpret that?

My whole reason for recording flat to begin with was to be able to do a perfect RIAA in the computer, not just to apply RIAA in the computer. The only way I know of to do this is record a pinknoise track off a test record using your flat preamp, then in the computer draw an RIAA curve using a powerful software eq such as the Waves Q10 so that a straight line is formed on your spectrum analyzer when frequency is plotted logarithmically against amplitude, which is plotted algebraically. If you haven't done this you aren't taking into account the frequency response of your cartridge and TT. And any change you make to your setup will change your flat recordings, necessitating a change to your RIAA curve, which means re-recording the pinknoise again with the new settings so you can change the curve.

You are right. We most certainly don't do this in the analog world, which is why I simply use a regular phono preamp now! I don't wanna be constantly fiddling with pinknoise, I wanna make CDs! The concept of computer RIAA is certainly cool IF you are striving for perfect RIAA. But it ends up being a lot of fiddling, and there are other factors involved as well. For instance, the self-made RIAA curve is ideal for flattening out the high end of an overly-bright cartridge to a perfect RIAA response, but the low end on an LP will vary. This is because during the mastering process most LPs were rolled off on the low end at anywhere from 50 to 75Hz! So you ask yourself "what is the point to all this"? If not making perfect RIAA in the computer, it's no better than using a regular phono preamp, as I've already said. And you need to have expensive software which won't have phasing issues when doing the conversion. That is why I recommended to Syra to use a regular preamp.

No, I haven't heard about the folks who are running their MCs at 1k-10k to heal the hi-frequency ringing. I would definitely like to know more about that! I've tried my new AT-OC9ML/II at 1k and it sounds pretty bad that way. I keep going back to 64ohms. The OC9 for me has a tendency to be really bright if I'm not careful. So far I've got 72 hours on it. I wonder if it's completely broken in yet? The high end is so much more detailed than that of my DL-103R that I want to keep using it. It also plays quieter and reveals no inner-groove distortion, also unlike the 103R. I already know I've got some albums which sound waaay to bright under it, and what I've done is use the Waves Q1 on them in the computer, applying a high shelf at 7025Hz to make them sound greeeat. But this isn't the solution I want, and it gets back to my new approach of getting the sound right before going into the computer.

 

[analognut]

Hi again Doctorcilantro-
I noticed your equipment notes say your digital out is an EMU 1212, so I've answered my earlier question. You must've just made a typo when you stated you record at 32/192. That's a 24-bit card, but it sure looks like a dandy! From what I can see, that is one of the best deals around! If I wasn't already over-spending I'd go out and buy one, although I only would use two channels. 

[doctorcilantro]

Right, i meant internal processing (if any) at 32bit but 24/96 is more accurate, sorry. I look forward to getting into this discussion some more with you all. I wish I had my stereo set up right now; we're moving things around big time and no serious listening for a while now.

best,
Jon

[doctorcilantro]

My whole reason for recording flat to begin with was to be able to do a perfect RIAA in the computer, not just to apply RIAA in the computer. The only way I know of to do this is record a pinknoise track off a test record using your flat preamp, then in the computer draw an RIAA curve using a powerful software eq such as the Waves Q10 so that a straight line is formed on your spectrum analyzer when frequency is plotted logarithmically against amplitude, which is plotted algebraically. If you haven't done this you aren't taking into account the frequency response of your cartridge and TT. And any change you make to your setup will change your flat recordings, necessitating a change to your RIAA curve, which means re-recording the pinknoise again with the new settings so you can change the curve.

Interesting, are the changes in VTA really going to affect the cart. calibration that much? If so, my MG-1 has a caliper to record VTA settings. I guess I could take readings for thin, medium, and thick LPs and try to establish 3 corresponding curves. I though the gist of what your describing here was more to create an EQ to calibrate the cart, but I guess it makes sense to do both (RIAA incorporating your cart's weaknesses) at once. Reading the DiamondCut documentation, I think they use set RIAA curves and a separate EQ that you "align" your cart with. Then there is room EQ which I'd like to get back into to doing on the playback chain in the 32bit realm, but I sold my ECM-8000 mic....

[doctorcilantro]

I investigated a lot of soundcards and the Echo 3G looked good but too bulky. The beauty of the EMU stuff is the Patchmix; it was really easy to keep the signal rather pure coming in and right back out via ASIO through Samplitude and the Lavry units. People will tell you go with Lynx or RME, but the funny thing is the Lynx L22 is getting old and uses the SAME EXACT ADC converter as the EMU 1212/1616....now the ADC/DAC chip isn't everything but after the Lavry AD10 I figure the 1616M should be fine AD duty.

DC

Right, i meant internal processing (if any) at 32bit but 24/96 is more accurate, sorry. I look forward to getting into this discussion some more with you all. I wish I had my stereo set up right now; we're moving things around big time and no serious listening for a while now.

best,
Jon

[analognut]

Doctorsilanto,
The AT-OC9ML/II has a micro-line stylus but doesn't seem that fussy about VTA, although I do like to keep an eye on it. Actually in my system (recently rebuilt Sota Star/vacuum with SME V) the OC9 seems very sensitive to small changes in dampening of the arm. Also the cart loading has a large effect on the sound. But I don't fool with the flat recording anymore. With the OC9 what would affect calibration the most is the hi-frequency spike so common to MC. I have been using the Waves Q1 (when you buy the Q10 you have the option of loading however many bands you need at the time) and set it to a high shelf cut on records where I just can't get the sound right any other way. The Q of the shelf is very low, only applying a little reduction at 7025Hz and maxxing out at the full -2db around 12kHz. I only have 2 carts and want to use the OC9 because it plays my older LPs so well.  Actually the spike is closer to 3db at 10kHz, but I always hesitate to use eq to begin with, so when I do I try to do it sparingly.. I am familiar with Diamond Cut's RIAA. To my ears it sounded fairly non-pro, as did their NR and most of the other stuff I'd tried. Thar's when I finally broke down and went all the way with the Waves software. 

[doctorcilantro]

Sorry, I have been busy with school, but all done finally!

Here's a little more about my setup and something I'm looking at trying to calculate.

There is a debate I was reading about running MC carts at 47K which opens them up; this had quiet a few manufacturers and experts chiming in, and I'm still looking for the thread.

Anyway, I great thing about using digital RIAA is it opens up the possability of using some really nice mic preamps which have specs would cost 3-5x as much in the phono preamp world.

So if, for example, I could load MC carts at 47K (or near that), it would open up even more possibilities for other equipment.

I'm trying to calculate, based on the following information, the load on my cart in my setup. I have wired my tonearm in a balanced configuration as described on PureVinyl site, AudioKarma, etc. and I utilize the following. I have some reading to do tonight but I thought I'd ping anyone interested.

Linear Gain AEA TRP ribbon pre:

36K input impedance

Grado Reference Statement (.5mv):

Inductance: 2mH
Resistance: 2
Input Load: 47K

Here (below) is an archived AA post in which the poster was using the higher output cart. I'm not sure about the capactance of my cable; it is very short maybe 1ft and, as mentioned, terminates with XLR (3rd pin no ground or connection to shield - although I have tried that). I get about -70db noise floor with about 70-75db of linear gain applied - this is prior of course to RIAA EQ which is done via a VST plugin in Samplitude. The AEA TRP ribbon pre is listed at 18K input impedance but I have verified it is actually 36K from the manufacturer. I have had the system offline for some time due to a move, but it sound really good before; right now I am just curious as to the resulting electrical specs.. I'm also planning to look into how the Grado low-output moving iron specs differ from those of a true MC because lately I have been reading about (here) an argument about using MC carts at 47K which would open up the possibility of trying some other carts with this mic preamp.

"GRADO
Inductance: 45mH
Resistance: 475
Input Load: 47K

I cannot reproduce here the VISUAL results of the program used to render the following calculation, but here are the results. They will, as have other real world tests, throw into question the rationale that drives manufacturers to provide a standard 47k load for MM cartridges, as well as the recommendation that users so load ALL MM cartridges (The Shure V15VxMR, for example, would not behave anything like we see here; their engineers seem to have designed it to work into a 47k load). Here are the results and something I think you might find worthwhile and relatively inexpensive to try out:

GRADO (45mH / 475d)

With 200pF cable & stray capacitance and 47K load resistor, output starts to rise at ~10KHz to +1dB at 20KHz and a +9dB peak at 50KHz;

With 300pF cable & stray capacitance and 47K load resistor it gets worse. Output now starts to rise at ~10KHz to +2dB at 20KHz and a +10dB peak at 42KHz;

With 200pF cable & stray capacitance and 10K load resistor things look much better. Output is pretty flat to 20KHz and rolls off to ?3dB at ~45KHz;

With 300pF cable & stray capacitance and 10K load resistor things look better yet. Output is ruler flat to 20KHz and rolls off to ?3dB at ~46KHz. In this scenario, the added capacitance actually helps.

Whether or not your ears will hear the peak (it is ultrasonic & outside the audible range), it is probably not good anyway. You WILL hear a difference, and I think one which you will find favorable, at least based on what information we presently have about your system and what you are now hearing as "wrong."

If you place a 13K resistor across the phono input plug, it will be in parallel with the existing 47K which is then 10K. It will let you experiment without modifying the preamp."

from http://db.audioasylum.com/cgi/m.mpl?forum=vinyl&n=196869&highlight=grado+impedance+47k&r=&session=

[doctorcilantro]

Good news.

 There are two  VST plug-ins for digital RIAA and the math is excellent.; I will post the other later.

 http://www.kvraudio.com/get/3550.html


 RIAA Filter software specs (of unpublished - but he says the math of the one above is comparable ):

44.1kHz

Maximum error from 0.00 Hz to 20000.00 Hz = ~0.224dB
Maximum phase error from 0.00 Hz to 20000.00 Hz = ~+/- 30 degrees

where the "phase error" is computed after a constant delay is added or subtracted to make the phase error equiripple

48kHz
Max error from 0.00 Hz to 20000.00 Hz = ~0.14dB

Max phase error from 0.00 Hz to 20000.00 Hz = ~+/- 24 degrees

88.2kHz
Maximum error from 0.00 Hz to 20000.00 Hz = ~0.0082dB

Maximum phase error from 0.00 Hz to 20000.00 Hz = ~+/- 3 degrees

96kHz
Maximum error from 0.00 Hz to 20000.00 Hz = ~0.0057dB

Maximum phase error from 0.00 Hz to 20000.00 Hz = ~+/- 2.4 degrees

One thought I had about compensating for the cart's curve is just do room EQ; the cart's error will not change and honestly I doubt my Grado Reference is going to be off that much, so maybe room EQ on the output is all we need as adjusted with a test record. Kill two birds with one stone.

Electrri-Q is a free 64bit EQ and these RIAA plug-ins are VST based for use in Sonar, Samplitude, etc.

DC

[doctorcilantro]

Syrah,

If you are recording through a flat-response preamp and applying a standard RIAA eq curve in your computer, then the sound will be slightly different (to my ears better) than recording the sound from the low-output MC run through the standard phono stage. But for the better sound you need to use the best software available in a 32bit Floating Point environment. I don't know what you're using, but a $50 editor will not do this.

The reason for the better sound is that most low-output MC have a peak in the frequency response at the high end and you are automatically correcting this when you adjust your software eq to apply a perfect RIAA curve, which I think is way cool, and you're automatically eliminating any other frequency deviations from the RIAA which may be introduced through your TT and cart setup. You would also be changing the signal to be absolutely flat all the way down to 20Hz, which is cool, but in the real world not necessary at all, since many recordings are rolled off during the mastering process at anywhere from 50-75Hz!

But you're still better off doing the RIAA with your phono preamp. For instance, if you make any adjustment to your TT which changes the sound even slightly, such as height of the tonearm, tracking force, damping of the arm, etc, you are then required to change your RIAA eq curve in the computer, and it turns into a big can of worms. You end up spending all your time recording the pink-noise track off your test record through the flat-response preamp so you can get your RIAA curve right again, and it's not worth all the time spent doing that. It ends up being a whole lot easier to just play the record with a normal phono preamp where you can listen to the sound as it's being recorded, and do the eq later, or not. My approach now has been to upgrade my vinyl front-end and make sure it's set up correctly. Then, if I'm not liking the sound of an LP I "tune it" by varying the cart load, VTA, VTF, and damping. But ultimately the idea is to find the combination which sounds right on (almost!) every LP. Then you know you've got it right, and you can spend your time making music and not fiddling!

When I was "into" doing the RIAA in the computer I tried plug-ins from all the manufacturers in my audio editor and the Waves software stood out as being ultra-transparent, very sweet-sounding, and without a doubt the best-sounding software I had ever gotten my hands on. I purchased enough of it as individual stand-alone plug-ins so that every single calculation that my computer makes is now done using a Waves plug-in.

Are you making CDs from LPs? If so, my recommendation is just use a regular phono preamp. Take the money you would have spent on the Q10 and apply that towards getting the Waves Restoration Bundle. Everything they sell is available free to try for 2 weeks, but buy from a pro-audio dealer at reduced cost.   

With an analog phono stage, different VTAs, let say three common ones like thin, medium, and fat (in reference to vinyl thickness) could be encountered. In these three encounters lets say the frequency response changes a little; maybe some carts more than others as some carts are bound to have more accurate FR than others.

So, with digital application you could, if you chose to, make three compensations with EQ for the cart and then apply the VST plugin for digital RIAA. So you would implement a particular EQ for the height of the record; if a record is cut differently, where the low end is rolled off, so be it, it is what it is.

One could configure a custom VST plug-in to mesh a particular cart's response with the RIAA curve; it would be much more accurate to do this in the "heavy-math" of the VST rather than an EQ no matter how good.

Diamond-Cut offers some older RIAA types but I haven't encountered a need for those yet.

One could simply live with the inherent error in cart frequency response (as one has to do in the analog realm), and apply a perfect RIAA curve in the PC. I understand your point that the result is not perfect due to cart error, but the curve itself is.

Audacity is free and can do 32bit float; not sure if it takes VST. You can just do it all free with MAX/MSP:

 http://www.head-fi.org/forums/f46/software-based-riaa-eq-part-2-a-311909/

best
DC

[doctorcilantro]

I'm also curious how you calibrated your cart? Do you use sweeps, tones, or pink noise?

I'd like to learn how to do it for when I get everything up and running.

thanks
DC

[analognut]

doctorcilantro-

To answer your question:
I mentioned in my 1st post of May22 on this topic that I use a pinknoise track from a test record to do the calibration. Also, since I quit using the flat preamp and am now using a regular RIAA  phono pre I have been using the Waves Q2 in the computer to flatten out the high end spike of the MC cart to a near-perfect RIAA by just using a hi-shelf filter. I use another band and also flatten out the low end from 20Hz to around 50Hz.

This really wasn't working out very well. I got the low end straightened out OK.  I was getting by with a shelf on the high end because I couldn't make the parametric fiilters do what I wanted them to do. A few years ago before I got smarter and started recording at 88.2 I used to record at 96kHz. Back then I was using the flat pre and I had no trouble at all getting the Waves eq to do what I wanted it to do. I think the problem has to do with the sampling rate of 88.2.

So I just gave up on the Waves eq for flattening out the RIAA. I got a hairbrained idea to insert a Behringer DSP8000 (31-band eq) in between the full amplified output of the phono preamp and the computer soundcard. It's a constant Q design, which uses dual 24bit processors, one for each channel. I then played a pinknoise track from a test record and adjusted the DSP8000 in realtime to give me an (almost) perfectly flat RIAA on the spectrum analyzer in my editor. I have been using the AT-OC9MLII long enough now that I know what loading, damping of the arm, tracking force, and VTA work well for me, so I don't change the TT adjustments and the sound stays the same as long as I make sure the arm is level on each LP. Honestly, I hadn't expected this trick to work properly, but it surprised the heck out of me. I got the RIAA flattened out very nearly perfectly and the sound is GREAT, so I'm happy with this setup.

It would be fun to try a high-quality mic pre like you are doing, and do the complete RIAA in the computer again, but the current setup is working out pretty darn well. It lets me listen properly to the music as I'm recording, and I drop markers whenever I hear any really loud pops which might require special attention later. 

[Syrah]

How do you guys run test signals from your turntable?  I've been trying to find the LP equivalent of the Rives test tones to no avail.  All the test LPs seem to do a tone sweep, which makes testing and adjusting my Driverack EQ impossible.  Thanks.

[analognut]

Hi Syrah- nice to hear from you again!

The calibration needs to be done using a signal which will produce a meaningful result on a graph so we can work with it. Pink noise is an audio signal wherein all frequencies are produced with the same amount of energy in bands that are proportionally wide. So a graph of pinknoise with amplitude plotted algebraically on the y-axis and frequency plotted logarithmically on the x-axis produces a perfectly straight line when all frequencies are being reproduced at the same volume. Now we have something we can work with, and the straighter the line, the more perfect your RIAA is.

I use the pinknoise track on the Hi-Fi News Analogue Test LP. Test records are really hard to come by these days, but this one is still available. Here is one place you could get it from:
http://www.tracertek.com/hifi-news-turntable-test-record
This company is the one that produces the DiamondCut software that doctorcilantro mentioned. They have an editor called DC7 which is pretty good. It has an analyzer which does a nice job of this. The program is downloadable for $99. It uses 32bit floating point math for the processing, which is a must, although it writes all temporary files to 24-bit for some reason. My current editor is able to write temp files in any format, so I just keep everything in 32bitFP. I used DC6 for years and liked it a lot when used with DirectX plug-ins such as the Waves software that I have. The DC6 sound was OK, but the Waves stuff is definitely better sounding. DC6/7 also has an "interpolation" function which is waaay cool. Using it you can zoom in on a soundfile and manually remove really big pops that are too big for automatic processes to get out. The result is astounding. It also has the ability to chain together numerous plug-ins and run everything together in one calculation, and lots more. It was not my intention to "plug" DiamondCut here, but it seems I have done so.

So the signal is fed from the LP on the TT through the phono preamp into the computer soundcard, and a software spectrum analyzer is used to graph the sound. Any analyzer which can display the x-axis logarithmically will work for this.   

[analognut]

doctorcilantro-

I was re-reading your post from July24 and am confused about what you meant when you stated: ...I understand your point that the result is not perfect due to cart error, but the curve itself is.

I know it can sometimes be easy to space out on this, but the whole point of making RIAA corrections in the computer is that you end up with a perfect response when you have achieved a straight line on your graph, since the pinknoise track was perfect to begin with. ???