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Tascam DA45HR

24-bit DAT Recorder
Published February 1999
By Hugh Robjohns

A 24‑bit, high‑resolution version of the DAT format allows users of 24‑bit workstations to transfer their mixes using readily available, cheap media.

Tascam's new DA45HR machine is not the first to try to extend the performance envelope of the original DAT format. Pioneer launched a proprietary format a couple of years ago with its D9601 recorder, which ran the tape at double speed to permit sampling at 96kHz with 16‑bit resolution. I suspect the machine succeeded more through its professional interface, reliable transport and general ruggedness than any significant sonic advantage, and no other manufacturer has felt the need to follow suit with a high‑rate sampling DAT recorder — so far...

Front view of the Tascam DA45HR 24-bit DAT recorder.Tascam's approach, by contrast, is to retain conventional sample rates but to offer higher bit resolution, creating a format which sits very comfortably with the plethora of workstations and digital sound consoles which are capable of 24‑bit resolution. Like Pioneer, Tascam have chosen to extend the data bandwidth of the tape by running it at double speed, so conventional playing times are halved — but then, a one‑hour, 24‑bit DAT master tape is still a very usable and remarkably cheap format!

DA45HR Features

As DAT machines go, the DA45HR is pretty conventional to look at and use; only a discreet logo on the tape drawer and the presence of a bit‑resolution switch give the game away. However, the machine is truly professional, and even without the 24‑bit option would impress for its feature list alone. This includes comprehensive digital clocking options, AES‑EBU and S/PDIF digital I/Os, balanced and unbalanced analogue I/Os (with calibrated and manual level controls), an optional wired remote controller, audible tape cueing, frame‑accurate locator memories, and a host of configurable operational modes. The only pro facility obviously missing is the ability to record and synchronise to SMPTE timecode!

Clearly, the DA45HR is a well‑specified machine even without the addition of the high‑resolution mode and it is certainly worth remembering that it can also be used as a conventional 16‑bit DAT recorder/player.

The rear panel is well-equipped with balanced and unbalanced analogue I/O plus AES and S/PDIF digital I/O.The rear panel is well-equipped with balanced and unbalanced analogue I/O plus AES and S/PDIF digital I/O.The rear panel is well equipped: analogue inputs are catered for with balanced XLRs and unbalanced phonos, as are the analogue outputs, both at +4dBu and ‑10dBV respectively. The balanced analogue outputs are complemented with screwdriver preset level adjusters. Digital interfacing comprises more XLRs and phonos, the outputs of both providing the either AES‑EBU or S/PDIF‑formatted data as selected from a menu. There is also a pair of BNCs providing a word clock input with a loop‑through, the latter featuring automatic 75(omega) termination. No word clock output is provided, as both digital audio outputs incorporate clock signals within the data stream.

A 25‑way D‑Sub connector provides a parallel remote facility with tally signals (including a configurable end‑of‑tape warning), and a serial data input. Although the handbook documents the wiring arrangements very well, it makes no further mention of the serial data control functions. A 3.5mm jack accepts the lead from the dedicated RCD45 remote controller. The only remaining connector is a standard IEC mains input.

Both mechanical and electrical specifications are very good, with a wind time of only 60 seconds for a 120‑minute tape, signal‑to‑noise ratio of better than 105dB (112dB in 24‑bit mode) and harmonic distortion below 0.002%. For reasons I cannot quite fathom out, the machine features Burr Brown 24‑bit A‑Ds but only 20‑bit D‑As, so true 24‑bit performance can only be realised through the digital ports using external converters. When using the internal analogue outputs, the 24‑bit recorded signal is rounded and dithered to 20 bits.

Operation

The DA45HR is as easy to use as any other DAT recorder with a draw loading mechanism in the top left corner, transport keys below and a large fluorescent display to the right. The configuration buttons and a shuttle wheel occupy the right hand side. A headphone output with its own volume control is provided in the bottom left hand corner.

A column of six slide switches on the extreme right set the principal operating characteristics of the machine.A column of six slide switches on the extreme right set the principal operating characteristics of the machine.A column of six slide switches on the extreme right set the principal operating characteristics of the machine. The first selects the digital clock source between internal, digital input, or word clock input. The next switch determines whether the machine operates as a conventional DAT or as a high‑resolution 24‑bit recorder (see box): operationally, there are no significant differences other than the halving of tape capacity.

The four remaining slide switches select the internal sampling frequency (44.1 or 48kHz only — no 32kHz LP mode), balanced/unbalanced analogue or digital inputs, AES‑EBU or S/PDIF digital input selection, and calibrated or user‑adjustable input levels for the analogue inputs.

The transport controls are entirely standard, with ID skip forward/backward keys and the usual arrangement of transport buttons, with Pause between Play and Record. There is also a record Mute key, and the wind/rewind keys can be set up to provide audible cue/review searches when pressed from play mode, if desired. Pressing the Record key on its own enters an input monitor mode where the display confirms the input arrangements and allows signal levels to be monitored, even with record‑protected tapes or no tape in the tray!

The large shuttle wheel allows the tape to be spooled with audible searching at between half and 12 times normal speed in either direction (eight times normal in HR mode). Within the search wheel is a 'data dial' used to alter parameters selected in the setup menus and determine tape start ID numbers for program playback.

To the left of the shuttle wheel is a group of 12 'command keys'. The button at the bottom right is a shift key to access alternate functions marked with blue legends above some of the other buttons (such as Locate store for the Locate memory buttons). The command keys determine such functions as the counter mode (A‑time, P‑time, remaining time, and tape counter), margin reset of the peak level display (which also resets the tape counter), and a Text display (the machine supports alphanumeric titles and labels stored on the tape).

The large shuttle wheel allows the tape to be spooled with audible searching at between half and 12x normal speed in either direction (8x normal in HR mode). Within the search wheel is a 'data dial' used to alter parameters selected in the setup menus and determine tape start ID numbers for program playback. To the left of the shuttle wheel is a group of 12 'command keys'.The large shuttle wheel allows the tape to be spooled with audible searching at between half and 12x normal speed in either direction (8x normal in HR mode). Within the search wheel is a 'data dial' used to alter parameters selected in the setup menus and determine tape start ID numbers for program playback. To the left of the shuttle wheel is a group of 12 'command keys'.A button labelled Display cycles through various other display modes which include the default program number and level margin display, a more detailed time‑display mode incorporating DAT frames along with hours, minutes and seconds, and a block error rate with separate readouts available for the A and B tracks/heads.

Other buttons enable skip play (recognition and activation of Skip IDs) and Auto ID writing during record, while an Enter button confirms alterations made to parameters in the setup menus. There are two Locate memories, and a Single Play mode where the tape plays until a new Start ID is found, then automatically stops.

The shifted functions include a repeat play mode, writing and erasing Start, Skip and End IDs, renumbering IDs, and editing location memories. It is also possible to program a playback sequence based on Start ID numbers, and to write up to 60‑character strings to label sections of the tape. The DA45HR stores these messages in the subcode on the tape alongside Start IDs, with which they are associated. However, few machines can actually recognise and display character strings, so they are of limited use.

Menus

There are 19 different menu pages on the DA45HR, accessed by repeated presses of either the Menu or Display buttons (the latter going through the list in the opposite order to the menu button). Before panic sets in, though, I should point out that some of the menus are actually just status displays such as logged head hours, and the rest involve only a single parameter — there are no multi‑level nested pages!

The menus allow the user to customise a wide range of operational parameters such as the Auto Start ID threshold (between ‑60 and ‑48dBFS) and the length of silence required to trigger the Auto Start ID (from 0.5 to 2.0 seconds). The relationship between the analogue interface levels and the DAT record level can also be adjusted for ‑16, ‑18 or ‑20dBFS to equate with +4dBu.

The digital output format for both digital I/Os can be selected between AES‑EBU or S/PDIF, and the output word length set to 24 or 16 bits (this is only relevant in the HR mode). A dithering option is available for the machine's analogue outputs when replaying 24‑bit tapes using the 20‑bit D‑A converters. The options are off, triangular or rectangular density distribution. Both dither modes reduce the technical signal‑to‑noise ratio but improve significantly the perceived sound quality, the best option being program‑dependent.

Another menu allows the copy‑prohibit status recorded on the tape to be set to allow unlimited copying, one generation of copying, or no copying at all (as per the SCMS requirements). The machine can also be configured to write an End ID every time it stops recording, and a further menu option determines whether, on encountering an End ID, the machine stops or rewinds the tape. There are quite a lot of transport‑related menus, setting such things as how many times the machine will repeat a passage if Repeat mode is selected (10 or unlimited), the pre‑roll when cueing to a locate memory (zero to five seconds), and whether the wind keys act as cue/review buttons or normal wind/rewind when pressed in play mode. When a tape nears the end, another menu sets the warning period (1, 2 or 3 minutes) for the End Tally signal available on the Control I/O port.

Since the tape runs twice as fast in the HR mode, but the tape format is the same as standard, the A‑time subcode on tape appears to run twice as fast as normal on high‑resolution tapes. A menu allows the machine to translate this code into a real‑time display if required. There is also a menu to reinitialise all settings to the factory presets, and a very useful facility to locate points on the tape where serious block errors have occurred.

Not really part of the menu system, but worthy of a mention here, is the comprehensive list of error messages which can be displayed — all of which are explained in the manual. These include warnings about incorrect clocking, problems with the digital I/Os, inappropriate tape (a tape recorded in 32kHz long play mode, for example), and some more serious technical problems, such as tape servo errors.

Listening

The Tascam DA45HR is an impressive machine. It looks and feels professional, solid and reliable, and it would be an asset in any control room. Good as the machine undoubtedly is as a standard DAT, however, the real reason for buying the beast is for its high‑resolution capabilities.

The only downside I can see to the DA45HR is that the HR format is unique to this machine, and so the chances are that you would have to take the machine into the mastering suite to replay your 24‑bit recordings. Assuming that doesn't bother you, the DA45HR does everything you would expect. Throw 24 bits of audio data at it from your digital console and it will record them perfectly well — I didn't notice any increase in tape errors beyond those normally expected from decent DAT tapes in a conventional machine... which is hardly any! Replay the tape into your digital console and everything is still there. What more could you want?

Compared to a conventional 16‑bit DAT (with appropriate dithering from a high‑resolution source), the DA45HR sounds cleaner, quieter, more detailed and more open. The gains are almost all in the subtle background noises and dying embers of sound — the things that make a recording come alive and sound more real. But if you are already working at 24 bits, you don't need me to tell you this do you?

Using the machine's own converters, it is harder to discern the advantages. The 24‑bit A‑Ds seem to be pretty capable — not quite in the dCS or Prism league, but easily good enough for most applications — and a whole lot better than those of a good many conventional DAT machines. I don't understand why Tascam have chosen to fit 20‑bit D‑As though, especially when the affordable Crystal 24‑bit converters have become almost an industry standard. Having said that, the D‑As are good, and the effects of tweaking the dithering can certainly be heard through them, but the advantages of 24‑bit recording are inevitably lost to some degree.

Presumably, the argument for configuring the D‑A side in this way is that anyone working at 24 bits must already have a decent 24‑bit converter as part of their monitoring chain, so why duplicate it? If this is the case, though, wouldn't the same argument also apply to the A‑D side as well?

There is no doubt in my mind of the advantages of 24‑bit resolution. For whatever reason — and the arguments still rage — it does sound cleaner and more precise than 16‑bit recording. And to this end, the Tascam DA45HR is a very useful machine to have in the control room, being very affordable, providing a familiar user interface, full backwards compatibility with conventional DATs, and 24‑bit resolution through the digital I/O. DAT media is also extremely cheap, even used at double speed, and has proven to be acceptably reliable. If you are a Pro Tools 24 user, this could be the affordable mastering machine you have been waiting for.

The only question left unanswered is, when will the quad‑speed 96kHz, 24‑bit DAT machine appear...?

High Resolution DAT

Tascam have obtained 24‑bit performance out of a 16‑bit format by a simple modification. The basic alteration is to increase both linear tape speed and rotational head drum speed — both by a factor of two — to provide the necessary bandwidth to allow 24 bits of audio data to be recorded during each diagonal tape stripe. Thus, in HR mode the tape runs at 16.3 mm/s instead of 8.15 mm/s, and the head drum revolves at a scary 4000 rpm instead of a still frightening 2000 rpm!

Obviously, increasing the tape speed by a factor of two halves the maximum recording time on a given tape, and so a standard 120‑minute DAT cassette (the longest Tascam recommend) will record 60 minutes of 24‑bit data. As the tape speed is different for the two formats, a single tape cannot contain both high‑resolution and standard formats, and a high‑resolution tape can not be played on any standard machine. The DA45HR recognises the tape format automatically and switches its mode accordingly.

Other than the double‑speed aspect of this proprietary design, the rest of the tape format remains largely identical to the original specifications — even down to the arrangement of the subcodes, which is why the A‑time display runs at twice normal speed during an HR recording!

When in standard mode, the DA45HR automatically reduces the data produced by its internal 24‑bit A‑D converters (or received via the digital inputs) to 16‑bit resolution.

Published February 1999