When Pure Vinyl ($229) was introduced a while back, I read a review that was published by a major U.S. based print publication. Software developer Channel D's claim to fame was that the signal from the turntable could be fed into the computer without RIAA equalization, and the program would handle equalization duties in the digital domain. The idea is that a cleaner, more accurate job of applying RIAA equalization can be done digitally, instead of the usual way of using circuits with physical parts. The only rub is that the audio signal must still be boosted to a level that the computer can work with. In this case, it requires a microphone preamplifier. Count me out- while I know high end audio well, I would not even begin to know the difference between a good or a bad microphone preamplifier. Besides that, I had been getting acceptable results using freeware (Audacity) to copy vinyl to my computer for use in my iPod Touch (and later iPhone 3G) or making CDs for friends and family from their LP collections.
As far as I was concerned, Pure Vinyl was an interesting concept, but I wrote it off and continued with my regular reviewing duties. Last summer, the big buzz in computer audio playback for the Mac OSX platform was Sonic Studio's Amarra, ($299 to $995) a program that works hand in hand with iTunes and OSX Core Audio to improve the quality of music playback. I contacted them to obtain an evaluation copy for review purposes. What I was offered was the same "cripple ware" demo version offered to consumers that would mute the audio every 20 to 30 seconds or so. This made comparisons between "regular" iTunes and Amarra impossible. Also, at the time, Amarra did not support Apple Lossless files, which many of my music files are. This issue has now been rectified. I want to also make it clear that while I did not expect a free copy of Amarra, I did expect something that could be used for meaningful comparison and evaluation, like a fully functional copy that would self destruct in a couple of weeks. There was no way I could continue with a review under those conditions, so I wrote Amarra off as well.
Very recently, I became aware that Channel D had added an iTunes playback feature to Pure Vinyl. Like Amarra, the recent upgrade allows for automatic sample rate conversion, but the appeal to me was that it is a memory player. Very basically, instead of transferring the data on demand in packets from an external hard drive via USB to the computer, the program will move the entire song (or album) into RAM and play it from there. Also, all of iTunes' audio conversion functions are disabled- Pure Vinyl can up sample the incoming data to 64 bit word length with up to 192 kHz sample rate, DAC dependent.
Leopard and Snow Leopard users are advised to download the pre release of Version 3, (Preview release 5a) from their download page, which is what I did. (Actually, I started with Version 4n4, which was replaced by version 5a to resolve an issue with gapless playback, which now works flawlessly.) What one gets is a fully functional program for a period of 15 days. After that, the program can be downloaded again to get another seven days. After that, pony up the dough if you like it. You don't work for free and neither do the folks at Channel D. While the pre release version does not have support for editing vinyl down to tracks or click and pop removal, the final release will. Obviously, these functions could not be tested. When I made vinyl transfers, I imported the files to Audacity to add track markers and repair the odd click or pop.
It is recommended that users download the software from this link. Registered owners are entitled to free updates as new versions are released.
Using Pure Vinyl is breeze. Start Pure Vinyl and once it is up and running, click on the iTunes icon on the Pure Vinyl opening screen. You will then see the Pure Vinyl docked to the left side of iTunes, as pictured above. At this point, use iTunes just as you would normally. When using Pure Vinyl, iTunes is just the user interface: the audio is handled by Pure Vinyl. The meters above the iTunes window can be deactivated if desired. The screen shot indicates that the user was using Memory Play mode but that the signal was not up sampled to 64 bits -- the display indicates "Native Sample Rate 44.1 kHz." Had the signal been up sampled to 64 bits, it would have indicated that, as below.
When playing 24-bit/96kHz files, it will say "Native Sample Rate 96 kHz" assuming the DAC supports it. I did run into an issue playing 24-bit/96kHz material via USB- because my DAC does not support that rate via USB, high resolution files played very slowly. All was well via the Havana's optical input.
There definitely was a marked improvement when using Pure Vinyl in 64-bit mode to handle the audio duties in all aspects- everything auditioned seemed to have a more lifelike presentation. Separation and definition of instruments was improved Resolution improved especially with female vocals (without becoming analytical.) Bass became more fleshed out, and imaging improved as well. Using a NOS DAC, I had no explanation for what I was hearing, that others heard as well, so I sent an email to Rob Robinson of Channel D. I received this prompt response:
"Pure Vinyl doesn't alter the audio (sample rate tracking mode), so it isn't hardware dependent. However, there may possibly be an advantage in using Upsampling mode with Redbook audio and the DAC receiving at 88.2 or 96 kHz, because Pure Vinyl's 64 bit internal SRC reconstruction filter, applied during re-sampling, attenuates content above 44.1 / 48 kHz, minimizing alias image generation in the audio range (because that DAC doesn't have a reconstruction filter).
If that's appealing, and your listening consists of a mix of Redbook and 96 kHz audio, then set the sample rate to 96 kHz. Redbook will be upsampled to 96 kHz, while 96 kHz audio will be passed through without alteration. The factoring sample rate converter in Pure Vinyl works equally well whether doing power of two or non- power of two conversions (the latter just requiring a little more CPU for processing)."
There is a third possibility, if the associated DAC supports a 192 kHz input, the signal can be up sampled to 24-bit/192kHz as seen below.
Those who have a large collection of vintage recordings will be pleased to see that Pure Vinyl supports many other EQ curves in addition to RIAA. Also, users can create custom curves if needed for playing back those discs that just "don't sound right" any other way.
I am certain that performance can be increased by bypassing the MacBook's soundcard, although I did not have the chance to do so. One caveat here, one must have the same bit rate and sample rate on input and output. In other words, if your DAC can only handle 16-bit/48kHz at its input, you will not be able to playback vinyl with a 24-bit/96kHz setting on your sound card. I did consider the Apogee Digital Duet as a relatively inexpensive ($499) solution to handle both input and output duties. Unfortunately I was unable to secure one to try out. Pure Vinyl will allow up to 192kHz sample rate, and recommends this for best performance. They are able to make suitable recommendations.
That said, the recordings made with Pure Vinyl are some of the cleanest I have ever made, regardless of recording media. Again, I know it would be even better with the correct associated equipment.
"We have gotten reports of the skipping problem you mention, and have recently been able to replicate it; it is related to an internal bookkeeping mechanism used to periodically confirm the play head position. This is a problem in the Preview that will be corrected in the next release."
I am, however, eagerly awaiting the finished release of Version 3. Keep an eye on this space, when the final revision of version 3 is released, Channel D has mentioned the possibility of sending one of their units to interface to mate to my MacBook so I can report on the full capabilities of Pure Vinyl for vinyl playback and recording.
We have received reports of USB DACs playing nonnative sample rate audio at the incorrect speed. This issue has been tracked down and will be corrected. The workaround, as described in the review, was using the optical output of the computer to drive the DAC.
Incidentally, the version 2.3 release of the Pure Vinyl editor can be used to create and split tracks at CD quality from high resolution recordings of vinyl made with either 2.3 or Pure Vinyl 3 Preview, by using the editor's high quality sample rate converter. The reasons for not supporting track splitting at high resolution are given on our website, and this limitation will be addressed in the final release version of Pure Vinyl 3.
Channel D also offers optimized flat-gain phono preamplifiers that provide an alternative to using a microphone preamp (and optionally provide simultaneous flat and RIAA-in-hardware outputs, the latter for times when it might be inconvenient to have a computer running). We also have many happy Pure Vinyl users successfully employing audio interfaces that include built-in microphone preamplifiers.
I'd like to mention a few things regarding RIAA correction in the digital domain, and Pure Vinyl's RIAA correction algorithm.
Some may be concerned or have heard that feeding the 'flat' signal from vinyl prior to RIAA de-emphasis will result in a reduction in digital resolution at low frequencies. It turns out this is not the case. An explanation is prohibited by space available here, but briefly, the RIAA filter enhances word length at low frequencies, in exactly the same way that the reconstruction filter used in DSD (SACD) recovers 24 bit audio from one-bit input. I'd invite anyone interested in the technical details to download (from our Pure Vinyl downloads page) a copy of the "white paper" on the subject (which was presented at the 2007 AES convention in New York City).
Finally, there are different ways to accomplish digital RIAA filtering, including some audio interfaces with plug-in DSP RIAA filters or EQ settings, usually implemented as FIR (finite impulse response or windowed) filters, which can impart a sonic signature of their own. In contrast, Pure Vinyl uses a three corner, first order IIR (infinite impulse response or continuous-time) filter, which is essentially identical to an optimally designed, conventional RIAA preamplifier filter in phase and amplitude response. This is one reason that once our users have tried flat playback and RIAA correction in Pure Vinyl, none have, as far as we know, returned to vinyl playback with a conventional phono preamplifier.
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