ã 1999 by Eddie Ciletti
MANUFACTURER: Tascam / Teac America; 7733 Telegraph Road; Montebello, Ca 90640; vox: 323-726-0303 faxback: 800-827-2268 web: www.tascam.com
APPLICATION: 24-bit Digital Audio Tape (DAT) Recorder
SUMMARY: Records 16-bit on Standard 4mm DAT or 24-bit in High Resolution (HR) mode at double speed.
STRENGTHS: 24-bit conversion can be optionally dithered — Triangular or Rectangular — to 16-bit. Consumer and Pro Inputs and Outputs, both Digital and Analog.
WEAKNESSES: Interface could be more logical, Captain! Transport should be able to handle "thin" tape.
LIST PRICE: $2,149
You know a manufacturer has struck Gold when a product creates enough of a buzz that people start calling this reviewer for an "advance opinion." That’s exactly what happened when the DA-45 24-bit DAT recorder ($2,149, list) was released last year. In 24-bit High Resolution "HR" mode the DA-45 runs at twice-normal tape speed, yet for some reason, the machine didn’t get into my hands any quicker! In this case, the delay worked to our advantage.
The DA-45 records in standard 16-bit mode as well. If you’re in a sailboat and don’t know which way the wind is blowing on the issue of "bit depth," click here for the Sidebar: How deep is the ocean (in bits)?
FREE TRADE AGREEMENT
Several of my friends, customers and acquaintances purchased the DA-45 well before my review unit arrived. Like them, you will appreciate the three "gifts" that 24-bits of dynamic range delivers. One: the security of recording at lower levels, knowing that resolution won’t be compromised. Two: Conservative recording levels increases the "distance" between the signal and the "over" gong. Those extra headroom "bits" provide a margin of safety, in case the band gets a little rowdy. Three: The additional resolution makes the stereo image more real.
Until the review machine arrived, I had to rely on feedback from the field, compiling a list of user-questions. The biggest complaint was the "fan noise" (detailed below). Everyone was curios about my opinion of the mechanism (See the paragraph "La Difference").
FAN CLUB
Because of the heat generated by the converters, Tascam felt compelled to include a fan. It’s not as noisy as most hard drives or computer fans, but considering how 24-bits relates to the potential low-noise floor, you’d think product noise would have been more of a consideration. The fan is a low-noise model by Panasonic, smaller but similar in design to the one used in the DA-88. Without the cover, it is actually very quiet. (There is now a fix. Please contact operational support 323-726-0303 ext 617.)
Like the DA-88, Tascam finds no reason to include a filter to draw CLEAN air into the unit. As a service technician I can say with authority that the original design will eventually draw airborne contaminants inside. The more obvious source of heat is the linear power supply. Had it been designed like the DA-88, most of its heat could have been dissipated outside of the unit. The head motor does have to run at 4,000rpm in HR mode (double the normal speed), though I had no way of judging its operating temperature.
YEAH! An Error Rate Display!!!
Using BASF DATmaster (49 minute) tapes I made separate 24-bit and 16-bit recordings each with very low error rates. One customer noticed that the error rate was higher in HR mode when compared to SP (16-bit) mode using a different brand of tape. (Click here for the Sidebar: Error Rate. In a future article, I hope to report on the performance of various popular tapes.)
MY TWO CENTS
If I were an Oyster, the grain of sand that I’d turn into a pearl would be the Interface on the DA-45. It’s not that much different from its predecessors and that’s exactly my beef. Since the original DA-30, I’ve felt there has always been room for improvement. Here are two examples to show how similar the DA-45 interface is to any Microsoft offering.
When the drawer is open the machine boldly displays "Tray Open!" (Thanks a pant load! Ya know, if I didn’t see it with my own eyes, I just wouldn’t believe it!) Put in a previously recorded 16-bit tape and you get the message "TapeMode NOR." (The machine will not go into record.)
Maybe I expect too much, like a message that explains, "This is a 16-bit tape. Overwrite in HR mode?" I appreciate the warning, but I think feedback — from the machine to me — should be less cryptic. After all, the microprocessor in the DA-45 is equivalent to an Intel 8088, the heart of a DOS-era PC. This is 1999, after all, and a tape machine should not require a visit to the porcelain office for manual ciphering… There should be enough internal brainpower to drive a display capable of providing full English sentences.
LA DIFFERENCE
After finally getting into the DA-45 I found the same ALPS mechanism Tascam uses in the DA-30 MKII, the DA-P1 portable and the DA-302 dual DAT recorder. OK, it’s not my favorite mechanism although TEAC/ALPS have addressed three of the four mechanical issues that plagued the original versions. (Sony’s transport in the PCM-R500 is better because it has separate reel motors and an all-metal mechanism. The ALPS mechanism is mostly plastic and reel drive "power" is via belt from the capstan motor. )
Tascam does not recommend "thin" tape, but consider this. A 120-meter data DAT can hold two hours of recording time in HR mode. (A two-hour audio DAT is 60 meters.) Now perhaps I’m giving away free product development advice, but HELLO? Why not use a drive that can handle thin DATA tape stock and not have to give up the two-hour recording time? The Alps Mechanism in the DA-60 has separate reel motors and, if mated with the DA-30 loading mechanism, it could be a winning combination.
In all tape machines, reverse-play is the acid test. If tension and tape-path aren’t spot-on, the tape will skew in the guides increasing recovery time (going back into normal play mode without errors) and potentially do damage to the tape. If you recall my Studer V-8 review (Feb’99), it turned out that five out of three hundred transports had that problem (after I tipped them off). What makes the DA-45 mechanism flawed is that there is no adjustment for reverse play. The DA-60 mechanism has this adjustment , allowing the tape path to be tweaked for gentleness.
THIS IS A TEST: PLEASE STAND BY
I made several test recordings simultaneously to the DA-45 and an SV-3700 (using the internal converters of each). The original analog source (the Mic preamp output) was also compared to the digitally converted signal. While the performance and the recording both sounded quite good, something in my monitor chain is impeding the ability to perceive the difference between the source and either tape machine. I made sure the levels were within 0.025 dB, changed cables and modified the test several times to help reveal resolution. I even borrowed a Bryston Preamp, which almost opened the "sonic revelation window," but I was expecting more drama!
It’s not my ears, because as recently as last week I heard the Prism 24-bit converter side by side with the Panasonic SV-3700 (at Studio Consultants in New York). The Prism was as close to matching the analog source, while the SV-3700 clearly revealed its age. (It’s an Imaging thang. See the sidebar: How deep is the ocean?) Of the people I know who are using the DA-45, one is especially particular about resolution, using external converters with no complaint about the machine’s ability to capture 24-bit data.
I can only promise to get to the root of my own resolution problem and share that precious info with you ASAP. At the very least it makes me wonder about the degree of resolution the average system is capable of delivering. Digital may actually be getting "good enough" to require that we reevaluate the analog portion of our systems.
Meanwhile, the DA-45 is the only 24-bit DAT available.
The street price should fall enough below the $2,149 list price making
the DA-45 — all idiosyncrasies aside — an affordable, transportable 24-bit
DATA STORAGE device for all those extra HR bits you’ve collected. If that
line leaves the marketing people a little flat, how about this one... So,
assuming you’ve captured reality, it can now be stored with a Tascam DA-45
without compromise.
TAIL OF THE DOG
Hindsight dates all the way back to the July’97 issue of EQ when I reviewed the Pioneer/HHB D-9601 DAT recorder. It recorded at 88.1kHz and 96kHz (in addition to standard sample rates). Back then I wondered why they didn’t go all the way — to 24-bit — and why I didn’t hear a difference between the normal and higher sample rates. Now I know!
Remember the concept of over sampling? Well, manufacturers have been sampling at higher rates for years because it solves two problems: filtering and its artifacts. (It’s our storage format that limits the ability to capture the higher rates in their "native" format.) With digital, it’s not possible to accurately record any frequency that is more than half the sample rate, A.K.A. the Nyquist frequency. Recording at 44.1 kHz limits the high-frequency recording capability to 22.05kHz. A filter that allows 20kHz to get through but not 22.05kHz has to be so drastic that its artifacts will "ripple" into the very audible range between 10kHz and 18kHz.
Over sampling — typically by 64x to 128x — relaxes the filtering requirements, generating artifacts well outside the audible range and therefore much less a cause for concern. As much as it would be nice to record at 88.2kHz or 96kHz, it doesn’t make as much difference (because of over sampling) as it does to increase the resolution from 16-bits to 24-bits.
TALE OF THE KAT(z)
It was Bob Katz who pulled me aside two AES shows ago to demonstrate the difference between 16-bits and 24-bits. You can "see" more bits because they help to make the stereo image more three-dimensional, more real, more like you could reach out and touch the acoustic sound source. I’m not saying you can hear this from across the room, but between two speakers, it’s obvious.
SIDEBAR: Error Rate
For as much emphasis as I place on the ability to monitor Error Rate, the way manufacturers collect and display this data does not always accurately reflect what’s on tape. There is a "window" within which the Error Rate can be sampled. The entire window is of the RF envelope, which includes one "swipe" of the A-head followed by another swipe of the B-head creating two separate areas on the tape and therefore two windows. A head-switching signal is synchronized with the rotational position of the head drum. There is enough room in the windows to accommodate four-head transports used in Time Code DAT machines with "confidence" heads.
In the center of the window is the main block of Audio Data. On the "outside" edges of the window is the "Subcode" information, which consists of Absolute Time, IDs and Status Flags such as copy protection. Only Fostex allows separate monitoring of Subcode, Audio Data or a combination of the two. Panasonic’s option is to show combined A- and B-head errors or just the A-head.
When the Adat XT when records over a tape originally made in another machine sometimes previously recorded hash shows up during the extremely narrow "transition window." That occurs when the head-switching signal toggles from A- to B-head. This hash cyclically shows up as increased errors even though this area is not used to recover any data.
|
|
Eddie |
the REVIEW List? |
|
|