Rane PaqRat

If you can live with losing four tracks on your digital multitrack tape recorder, the Rane Paqrat will allow you to record with up to 24‑bit resolution. Hugh Robjohns rates the 'rat.

An increasingly common requirement among the professional recording fraternity is to record with greater dynamic range than conventional 16‑bit equipment allows. The supporting argument is that if the domestic replay medium has 16‑bit resolution, the origination format should be somewhat better, such that a generous headroom can be allowed during the original recording (to cope with unexpected peaks) while a very low noise floor is maintained. Subsequent post‑production and re‑mastering to a 16‑bit domestic format will therefore not degrade the quality of the material in any way, and may actually enhance it if noise‑shaped re‑dithering systems such as Sony's SBM (Super‑Bit‑Mapping) or Deutsche Grammophon's 4D processes are used.

The majority of classical recording labels are routinely using 20‑bit A/D converters these days and some are using devices with even greater resolution. Although suitable equipment to perform the analogue‑digital conversion at 20‑bit resolution (or higher) is widely available, there remains a problem over which digital recording format to use. Surprisingly, recording formats offering 20+‑bit capability remain quite scarce. There are a couple of devices that use magneto‑optical disks (from Sony, Genex and Studer, for example); tape‑based formats include the Nagra‑D, and the latest 24‑bit DASmachines from Sony, and then of course there are several digital audio workstation systems. However, all of these options are relatively expensive and so make it hard for the home‑studio owner or amateur sound engineer to take advantage of recent improvements in analogue‑to‑digital conversion technology and pricing.

The ideal solution would be if someone made a unit which could remove the 16‑bit restriction of affordable multitrack formats, such as ADAT or DTRS (the Tascam DA88 format also supported by Sony; it stands for Digital Tape Recording System), and allow high‑resolution recordings.

Paqrat

Well, if you've read this far, you will have guessed that such a device is available! The Rane Paqrat encodes a stereo AES‑EBU or SPDIF signal, of up to 24 bits per channel, onto four adjacent tracks on the multitrack tape (user selectable between 1 and 4 or 5 and 8), formatting the data so that it conforms with the 16‑bit structure of the appropriate ADAT or DTRS tape format.

The idea of trading tracks for resolution is not new — other manufacturers have already produced similar products for the professional DASmultitrack machines as well as designs for ADAT and DTRS. However, the Paqrat is affordable and well engineered and has a couple of very useful features.

Two versions of the Paqrat are available: the RC24A interface is designed for ADAT machines, and the RC24T is equipped to suit DTRS‑format machines (DA88s or PCM800s).

Hardware

The two versions of the Paqrat are identical apart from the machine‑specific connectors on the rear panel. The case is a 1U rack‑mount steel box, 21.5cm deep. AES‑EBU digital inputs and outputs are provided with standard 3‑pin XLR connectors, and a 24‑bit SPDIF input is available via a phono socket. Input selection is performed by a push button on the rear panel next to the connectors.

The RC24A version of the Paqrat has a pair of TOS‑link‑style optical connectors for record and playback links with an ADAT machine, whereas the RC24T version has a 25‑way D‑sub TDIF connector, plus a BNC socket carrying the word‑clock, to interface with a DTRS machine.

The interfaces are powered by an external transformer unit (with screw‑down brackets) but the review model was fitted with a 2‑pole European‑style mains plug. The transformer provides a centre‑tapped 9V AC supply through a six‑way latching plug which looks very similar to the standard telephone plug. Fortunately, this is actually a little smaller than a normal phone plug, so it won't mate with a telephone socket — I tried! There are no fuses on the mains or low‑voltage sides of the transformer (other than in the plug‑top if you fit a UK mains plug). Next to the PSU connector on the rear panel is a suitably marked screw which provides a chassis earthing point if needed.

Inside the Paqrat there is a great deal of empty space — so much, in fact, that the depth of the unit could have been 9cm less (or the mains transformer could have been built into the box). There are two high‑quality circuit boards inside the unit, one immediately behind the front panel carrying the switches and indicators, and the other behind the rear panel carrying the socketry and all of the electronics.

All seven of Paqrat's integrated circuits are mounted in sockets, and should it become necessary to update the v1.0 operating software, access to the EPROM chip is very straightforward.

Front Panel

The controls on the front of the Paqrat are very simple and entirely self‑explanatory. On the extreme left, a yellow LED indicates an acceptable power supply, and next to it is a pair of green LEDs which show the presence of an input signal (labelled 'Sync') and suitably connected tape machine ('Transport Present').

Moving along to the right, a push button selects which group of tracks the input signal will be recorded on (1‑4 or 5‑8) — the selection is shown on a pair of LEDs — and a second button (labelled 'Both') routes the input signal to all eight tracks simultaneously (making a redundant safety copy of the recording on the same tape). Further to the right of the panel, another push button with associated LEDs selects the replay group of tracks (again 1‑4, or 5‑8).

The right‑hand half of the panel has a collection of LEDs to show the input signal sampling rate (44.1 or 48kHz) and word length (16, 18, 20, 22, or 24 bits). The extreme right of the panel contains the final push switch which truncates the high‑resolution off‑tape digital output to 16 bits but re‑dithers the signal properly so that there are no nasty quantisation distortion products. This useful facility could be used to make 16‑bit 'demo' tapes on convenient formats such as DAT or CD‑R, while recording a 20+‑bit master.

In Use

The Paqrat performed very satisfactorily: it certainly coped with a 24‑bit test signal perfectly well, and the 16‑bit re‑dithered output was fine.

I have only two criticisms: firstly, external mains transformers are my pet hate, and there is plenty of room inside the box to have a proper built‑in power supply. Secondly, it seems rather sad that there is no means of accessing the second group of four tracks while you're using the Paqrat to encode 24‑bit signals on the first four. I see no reason why the Paqrat can't have two 24‑bit inputs so that four high‑resolution channels could be recorded simultaneously. Alternatively, standard 16‑bit access to the remaining four channels would have allowed additional low‑resolution tracks to be recorded along with the 24‑bit stereo signal. Niggles aside, though, all in all the Paqrat is one of those very boring products that just does what it is supposed to without fuss or drama.