"DJ" turntables and digital output
 

The so-called "DJ" turntables seem to represent good value, especially for those of us dealing with 78s. I'm very happy with mine.

One thing I like is having the cartridge preamp built into the turntable. It seems to me that the shorter the wire between the cartridge and the preamp the less susceptibility you have to hum. Mine, in common with most, gives you a choice between phono-level output (unequalized), line level, and digital out. I plan to make use of the digital output when I get a new sound card next week. Here's what I'm wondering.

Does anyone know whether these preamps are performing RIAA equalization in the digital domain or in the analog domain? If in the digital domain, are they generally more accurate than their analog brethren?

(Off topic: I also like being able to raise the tonearm. When I have an off-center pressing I just add some extra turntable mats to get even with the top of the spindle, center the record, and raise the arm to match. Works pretty well.)

What is the brand and model of the turntable? I do not know the answer to your question, but I would suspect that anyone with information about this will need to know that data. I suspect that it may be a Stanton. Please advise.

Equalized or not
 

Theoretically, I agree with the assumption that the closer to the cartridge you can create a line level or digital signal, the less chance you have of picking up hum. This is balanced by another theoretical consideraton or two.

The first consideration is how "flat" a file can I get by allowing the turntable to apply an RIAA curve, either at the analog or digital stage and then negate that equalization in DC using the reverse RIAA filter. I agree with your assumption that you'd be better off if it is applied digitally, but either way, chances of you passing the signal through a filter and then an "unfilter" and coming out with a signal near the original flat signal are slim. I have some indirect evidence to back this up. My soundcard accepts a phono input and applies no RIAA, therefore providing me with a flat signal. The soundcard came with software with a "switch" to apply RIAA. The results from this EQ is very different from the EQ using DC and the RIAA preset. I'm sure that DC is more correct, but it shows that you can't ever be sure of what you're getting.

The second theoretical consideration is whether or not I'm more likely to introduce audible distortion or anamolies by running the file through two filters instead of one. Let's be real. With modern equipment, properly grounded, the hum should be so low that it's unimportant compared to the noise from the source material. If you're going to have to apply another filter, you might try something I did. I placed the needle in the run in groove of a 78 with the platter still and recorded 30 seconds of sound. I did the same for LP's. I then took the resultant files and did a sample with the continuous noise filter. I sometimes, not always, apply this filter as the first in a continuous noise filter chain.

There's one last consideration I think you need to make. Check the specs on the digital out from your turntable. For those TT's for which I can find specs, the output is 16/44.1. Many of us have found that the filters, such as the impulse filter, give better results on 24/96 files. For whatever reason, I seem to be able to be more aggressive on my settings before introducing distortion.

I think you might want to seriously consider one of the Tracertek's phono amps that provide a flat signal and use the analogue phono out from your turntable. Whatever you do, please let us know the results.

BTW, which TT do you have? I'm looking at the Denon DP-DJ151 Direct-Drive Digital Turntable (http://www.musiciansfriend.com/srs7/...se_pid/808005/). I've read information saying that it shares many components with the venerable Technics 1200, including the tonearm. If true, it's a real bargain at $300.00. That's about what I paid for my used Technics SP-15 (which I really like). I'm still trying to figure out how to explain to my wife why I need two platters. :D

Doug

You suspect correctly. STR8-100 to be exact and actually an arbitrary choice. The salesman was an idiot full of incorrect information and I just went by price ($300) and brand name. The documentation provided was sketchy at best and, for some reason, it didn't occur to me until typing this to see if there's any technical background at their web site. [Just checked. There isn't.] I was just looking for something reliable to replace my Thorens which would pick its own RPM out of thin air (sometimes in the middle of a record) when it was set to 78. I'd already had it repaired once and figured I'd be ahead buying a new unit. Heck, I even like being able to play records backwards. It does help sometimes with disks with damaged grooves that skip, not that you can't do it manually. Getting a turntable with a short straight arm was a mistake though, and there's no antiskate on this model.

HB

I think you've written an article about this, and I hear what you're saying. I'll just respond that it's not a practical consideration for me at this time. Maybe in a year or two.

One reason it's low priority right now.

Cool idea. I have a preset made before I got DC 6 which was created from a 1938 record with an amazing amount of lathe rumble and some hum. I preprocessed the waveform to isolate the low end noise, isolated it further when I made the noiseprint with the noise filter I was using at the time and now use it frequently as my "rumble filter." (The noise filter is a plug in, so I can even use it in DC 6---with that noiseprint.) It does an amazing job with some material.

Just the information I don't have. I guess DJs don't get off on that kind of thing. They're mostly interested in fast starts and matching keys between different recordings I suppose. But you're almost certainly right that it's 16/44.1 and I am anxious to try declicking and maybe noise reduction at higher resolution. Your manual says it's only relevant for declicking, though. Have you reconsidered that position?

Good luck with that! Just looking at all those DJ tables, I'd say they share most of their components. I was just looking for a DJ turntable review I found on the web last month and, unfortunately, couldn't find it. The turntable was being compared to the 1200 and the reviewer found it superior in almost every respect. It was one of those 25,000-word essays with all kinds of esoteric tests, plots of test results, and so on. The main point of all the jabber was to demonstrate that belt drive is much less important than solid engineering and can introduce anomalies of its own. As I say it's unfortunate that I can't find the review because I can't even remember the brand name although my local electronics store carries it. One thing that makes me salivate is that it has a digital readout of playback speed. No strobes needed to set any speed you need.

Thanks for the information.

HB

RIAA on Turntable
 

Hi guys,

We sell the stanton ST-100 on Tracer and the RIAA is applied before it is digitized and send out the digital out. The only dsp algorithm on board is a speed change/pitch change function. As with all RIAA implementations done with resistors and caps, there are imperfections in the RIAA curve - likely small, but a real analysis would be hard since you'd have to do it without a cartridge.

In our opinion, bringing it in flat and then applying the DC Six RIAA is the best approach. Not only is the RIAA dead on, but you don't get the phase problems associated with any R/C EQ implentation.

Thanks, Curtis. To tell the truth I asked more out of curiosity than anything else. Frankly, with 78s the only touchstone that makes any sense to me is, "What would this have sounded like if you could have heard it live?" If I can get something that sounds real within the limitations of the mic setup and studio acoustics, I don't care that much about whether the "flat" version is dead on or not. Heck, if the RIAA version sounded more realistic, I'd use it right or wrong. But my experience so far has been that although the RIAA often sounds great, other turnovers sound more realistic.

If there were some way to know what the recording engineers heard or wanted us to hear, then I would shoot for that I suppose. But then maybe they would have been shooting for what the general public would have heard on their Silvertones, Philcos, and Stromberg Carlsons. And what kind of reference is that? In the end, it's all subjective.
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So who makes those inboard preamps on the various DJ turntables? Are some of them generic OEM units? Do any of them do anything digitally beyond pitch-shifting?
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And, since you know the turntable, is it normal to get hum when the arm is outside the platter, or do I have an internal grounding problem or something? It goes away when I'm over the record, so there seems to be some source of hum on the tonearm side of the case. (Grado cartridges.)

HB

Please keep in mind that RIAA compensation did not apply to 78 RPM records (it was only used on vinyl 33's and / or 45's). Those 78's recorded before the electrical period (in other words, acoustically and before 1924) had no equalization / compensation. Those made during the electrical period (post 1925) used a "turnover" frequency compensation only (no rolloff). Please refer to the back of the Diamond Cut Users Manual for details about the various turnover frequencies which were used by the various manufacturers of 78 RPM records. The chart is in the appendix section. These curves can also be found in the Diamond Cut Paragraphic EQ preset listing. Playing a 78 RPM record through an RIAA pre-amp circuit will tend to sound "dull" on the top end of the spectrum and the bass could sound either too heavy or too light depending on the brand of record.

If you transfer a 78 with an RIAA pre-amp one of the following compensations is suggested:

1. Reverse the RIAA Curve using said curve in the Paragraphic EQ and then apply the appropriate Turnover frequency for the brand of record.

2. If you keep it as an RIAA transfer, then use one of the EQ's to kick up the top end of the recording until it sounds more natural to you.

3. If you use method number 2, you will also need to adjust the bass (frequencies below 500 Hz) until the transfer sounds natural to you.

That's what I do. Of course I run into my share of undefined labels like Sonora ("Clear as a Bell") and Philharmonic (cutting 4 minutes on one side of a shellac 78 and anything but "Clear as a Bell"). So all you've got is your ears. So I just try to figure out what the most popular curve was and use that as a starting point. I almost never try to "enhance" the bass because it tends to sound muddy toward the end of the record when you run into what I call the pinch effect. But DC 6 has the tool for that job and, when I get back into working on records, I'll probably start revisiting that subject as I rerestore some of the records I did with other software. I've never been entirely satisfied with my efforts that way, especially when the end of one side has to segue directly to the beginning of another. It's especially nettlesome when you're dealing with spoken word recordings.

HB

I understand. The end of one record will have much less bandwidth than the beginning of the next, and so the rub. As you allude to, the Diamond Cut Filter sweeper can be used to remediate this problem.