This mid‑priced DAT shares some rather higher‑class innards with its more expensive siblings, and is also equipped with Sony's Super Bit Mapping technology for improved noise performance. Hugh Robjohns checks it out.
The DAT machine has become the default stereo recording format for most home musicians and semi‑pro studios. Sony created the format for domestic use but, for one reason or another, it never made it — instead, it's been adopted by broadcasters and music studios. While some of the top recording studios remain sceptical about the format in terms of the interchangeability between machines, and its general reliability, it's safe to bet that you would find at least one DAT machine in every control room.
The Sony DTCA9 DAT recorder reviewed here is positioned halfway between the domestic and professional machines in Sony's catalogue and is really a minor development from the DTCA8. However, it shares a lot of its internals with the up‑market PCM2600 and 2800 machines, including a four‑motor direct‑drive transport and the ability to record at 48, 44.1 or 32kHz (the last in a 12‑bit non‑linear long‑play mode).
The Box
The DTCA9 is modelled to match the all‑black domestic hi‑fi styling that Sony have been using for a few years now. The machine conforms to standard hi‑fi sizing, 17 inches wide and 5 inches high, so it will look at home among other stereo equipment or will fit into a standard 19‑inch rack. The good news is that it's supplied with a set of substantial rackmount ears and a 'decorative panel' to conceal the feet. At 14 inches, the A9 is quite deep: you'll need to leave additional space at the back for the mains and audio connectors. The machine weighs a touch under 14lb.
All inputs and outputs (except the headphone socket, of course) are on the rear panel and you have the choice of balanced or unbalanced interfaces; the balanced connections use XLRs and the unbalanced are on phono sockets. A small slide switch selects which type of input connection is in use, but all outputs are active simultaneously. A very useful feature on the A9 is provided by screwdriver trimmers adjacent to the XLR connectors, allowing you to align the record sensitivity and output level to a house standard. As supplied, the machine is set with a very generous headroom where 0dBu equates to ‑24dBFS (the EBU standard is ‑18dBFS), but this can be adjusted anywhere up to ‑8dBFS.
The rear panel also carries a set of digital interfaces in the form of co‑axial and optical S/PDIF connections. The recording input is selected on the front panel by a three‑position rotary switch, allowing a choice of analogue, optical digital or co‑axial digital inputs. It would be nice if the analogue position was replaced by separate selections for unbalanced and balanced analogue inputs, but you can't have everything, I suppose!
The machine is SCMS‑equipped, so you can record a copy‑prohibited master (commercial CD, for example) over the digital interface to make a true clone, but you cannot copy the clone to another digital recorder digitally. True professional machines don't have to incorporate the SCMS system (the A9's big brothers, the PCM2600 and 2800, don't use SCMS, for example), but because this machine falls into the domestic category, SCMS is a legal requirement.
A footswitch can be connected to one of two standard jack sockets on the rear of the machine to perform a number of useful functions. The first socket is labelled Rec/Pause and each press of the footswitch simply toggles the machine between the record‑pause mode and actual recording. The second socket is labelled Mode, and the function of the footswitch is determined by a three‑position slide switch on the left of the front panel. The first mode is a simple play‑stop‑play function, each press of the footswitch activating the next operation in the cycle. The second mode includes a review facility when the machine is playing: when you press the footswitch, the tape is wound back about 15 seconds and played again. The last mode replaces the review function with an AMS search, so that the tape winds back to the previous Start ID and stops. All of these functions are very useful, giving hands‑free operation when you're trying to learn a piece of music or rehearsing against a backing tape.
The mains power connection is via a standard IEC socket rather than a captive lead, but I was surprised to find that the review machine was equipped with an IEC mains lead with bare wire ends rather than a moulded 3‑pin mains plug. Also supplied was an infra‑red remote control handset complete with a pair of AA batteries, and a set of phono‑to‑phono leads.
Black Buttons On Ablack Background
Whenever I look at black hi‑fi equipment I always recall a line from the Hitchhiker's Guide to the Galaxy where Zaphod Beeblebrox tries to steal a spaceship but is confused by the ship's control panel — black buttons on a black background, which light up black when you push them. Sony's A9 could have been designed to the same philosophy. Fashionable it may be, but it's also very awkward to use in a dimly lit control room — thank heavens for the remote control!
The left‑hand side of the machine carries the cassette door, with the mains power button, infra‑red sensor, and a couple of slide switches to its left. The two slide switches control the operating mode of the footswitch and engage the SBM (Super Bit Mapping) circuitry for analogue recording (see box below).
The main transport controls are arranged in a strip below the meter display, together with the usual Start and Skip ID facilities. The machine performs an automatic End search if the Fast Forward button is pressed in Stop mode. Also in this section are a couple of buttons to cycle through the time display modes and reset the tape counter, as well as a button that resets the recorded level margin display (a numerical readout of remaining headroom).
The meter section is a blue fluorescent display providing numerous information labels, a horizontal bargraph level meter, and a time display (showing either A‑time, track time, remaining time, tape time, recorded date and time, or current date and time).
To the right of the meter display is a keypad for direct track access and some programming keys to set the internal clock and organise the Skip‑play functions. To the right of the keypad are two rotary switches selecting the input source and sampling rate, and on the extreme right is the record level control. Below this knob is a headphone socket and a separate listening level control.
In Use
I find it hard to get excited about DAT machines these days but, as DAT machines go, the DTCA9 is an extremely competent one, with well thought‑out facilities which would integrate well into any semi‑pro studio. The transport is well built and I experienced no problems at all with its tape handling, which was fast, quiet and easy to control. The inclusion of balanced analogue connections is useful, especially alongside the DTCA9's ability to align input and output levels to your own house standard. It would have been nice if the balanced/unbalanced input selection was available on the front panel, because this would have made system integration that little bit more flexible, but this is really a very minor complaint.
Sound quality is to a high standard and the A/D and D/A converters are very good indeed. The SBM process works well, although its benefits seemed to vary slightly with the type of material being recorded. If you can live without balanced I/Os, you could check out the otherwise identical A8 (or junior A6) machine, and if you need AES‑EBU digital interfaces and freedom from SCMS, look at the PCM2600; the top‑of‑the‑range PCM2800 extends the family's capabilities with a four‑head design giving off‑tape confidence replay. In fact, this whole family of DAT machines can be recommended, not just the DTCA9 — which is, on the whole, a good machine and one that should prove ideal in its intended market sector.
Super Bit Mapping
The idea of the SBM system is to reduce the apparent level of quantising noise from the A/D converter, during recording, by some clever technology (generically called 'noise‑shaped re‑dithering'). It may seem rather odd to want to improve the noise performance of a system that's already pushing ‑96dB, but the proponents claim a more 'expansive' sound — SBM certainly does work and its side effects are very benign, so why not?
Basically, the analogue signal is converted into digits by a high‑speed A/D converter which works a little bit like a backwards oversampling system. The analogue audio is sampled at a high rate (many times higher than 44.1 or 48kHz) but with limited quantising resolution (typically, just a few bits). This data is then passed to a 'Decimation Filter' which converts the excessive sampling rate into much greater quantisation resolution.
In the case of the DTCA9, each 44.1 or 48kHz sample falls out of the A/D stage as a 24‑bit word, but the DAT format can only record 16‑bit words. Obviously, the bottom eight bits of the A/D output must be removed — a process which must result in an increase in quantising noise (a 24‑bit signal is a lot quieter than a 16‑bit one). However, by re‑integrating the unwanted data bits with the original signal (in much the same way as the remainder is added back in when performing long‑division), the process retains much of the extra resolution of the 24‑bit signal.
The discarded data bits pass through a digital filter before re‑integration. This filter shapes the frequency response of the quantising noise to reduce its level in the 3‑4kHz region, where human hearing is most sensitive. If the noise is reduced in one area, it must be increased in another (no free lunches here!), and the SBM system boosts the quantising noise in the extreme high‑frequency end of the audio spectrum, where human hearing is less perceptive.
The theoretical noise improvement afforded by SBM is of the order of 10dB below 3kHz, reducing to 4dB below 12kHz. Above 15kHz the noise performance is actually worse (rising to almost 20dB at 20kHz), but it's claimed that this is inaudible.
Super Bit Mapping is a one‑off process and requires no decoding. From a technical viewpoint, it doesn't improve the basic performance of a 16‑bit system — if you were to measure the broadband noise of an SBM recording it wouldn't be any better than a straight 16‑bit recording. However, it sounds better to the average human listener, which is really what counts, isn't it?
There are other systems in commercial use that use similar strategies to reduce the apparent noise performance of 16‑bit systems. For example, Deutsche Grammophon use a system they call 4D to convert 21‑bit master recordings to 16‑bit CD releases, and I believe that Decca have a similar un‑named system, which they've been using for some time.
Pros
- Easy and intuitive to operate.
- Reliable mechanics.
- Flexible analogue/digital interfacing and remote control options.
- Good sound quality.
Cons
- Front panel can be tricky in low‑light conditions.
- Rear‑panel selection for analogue input mode.
Summary
A solid and dependable DAT machine with excellent transport and a good range of facilities. Balanced analogue interfaces with adjustable levels are appropriate on a machine in this sector and the rackmount kit that's included is very welcome. A/D and D/A converters are of a high standard, further improved by the inclusion of the SBM analogue recording process.