Apogee Mini-Me

Two-channel Preamp & A-D Converter

Published in SOS June 2003
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Reviews : Preamp

Photos: Mike Cameron

Two-channel Preamp & A-D Converter

This compact unit from Apogee offers high-end preamplification and conversion, along with a clutch of useful processing, monitoring and output facilities.

Apogee have enjoyed a long association with high-quality digital audio, stretching back 20 years. In the very early days of commercial digital audio, Apogee made replacement brick-wall filter modules for the first generations of Sony CD master recorders. Having improved the audible quality of anti-alias and reconstruction filters, the company went on to build many excellent complete A-D and D-A converters which were often used as reference units by CD mastering engineers. Some models were specifically designed to provide alternative interfaces for various third-party systems — for the Pro Tools DAW and Yamaha digital mixers, for example.

Apogee also developed the UV22 dithering system which was incorporated in their converters as well as being made available later as a stand-alone software plug-in for various DAWs. UV22 quickly became the industry standard bit-length reduction tool for many years, and is still highly regarded and widely used today in its UV22HR form.

The latest addition to the Apogee product line is the aptly named Mini-Me, a portable dual-channel A-D converter with built-in microphone and DI preamps. Apparently, the Mini-Me resembles the earlier Apogee AD1000, with a similar extruded case and purple control knobs, although I have not had the pleasure of using that particular machine. However, while the externals many appear vaguely similar, the internals are definitely all new, with 24-bit/96kHz capability and a USB port to enable direct interconnection with a computer.

Apogee Mini-Me £1291 pros Quiet mic preamps and good DI input. Calibrated line inputs. Soft limiting and new Push-It compressor functions. Output resolutions span 16-bit/44.1kHz to 24-bit/96kHz in AES-EBU and S/PDIF formats. USB output at 44kHz or 48kHz, via built-in SRC. Direct and USB return monitor mix with mono facility. Can be powered from battery supplies. cons No facility to link channel gains for stereo applications. Crude metering. No external word-clock input. summary A compact but high-quality A-D converter with mic/line/DI input facilities, preset compression/limiting, monitoring facilities, and a USB interface. "The Mini-Me's performance is little short of astonishing, given its size..."

This really is a very compact little unit, measuring 4 x 14 x 25cm (hwd) and weighing just under 1kg. The extruded two-part case is held together by Allen bolts on the front and rear panels, so gaining access to the internal electronics is fairly straightforward if required. Most users won't need to get inside, but there are some user-configurable settings here, such as the facility to reduce the maximum microphone amplifier stage gain and adjusting the Push-It compressor ratios, of which more in a moment.

The rear panel is very simply laid out, with a couple of combi jack/XLRs to accept XLR or TRS jack plugs for microphone, line or DI inputs. The main A-D outputs are provided simultaneously in AES-EBU and S/PDIF formats on XLR and phono sockets, plus the B-type USB port. The AES-EBU and S/PDIF sockets support single-wire operation at the elevated sample rates of 88.2kHz and 96kHz. However, the USB port only supports rates up to 48kHz. There is also a 3.5mm miniature headphone socket for monitoring purposes. The last connector on the rear panel is a coaxial DC socket which draws 5.5W of power from any 6-14V DC supply. A 12V in-line switched-mode power supply is included with the Mini-Me, and various suitable battery packs can be obtained from third-party suppliers.

The front panel is surprisingly simple given the flexibility and capability of this machine. The unit is switched on by a toggle switch in the top right-hand corner which offers three modes: off, on, and on with phantom power. An associated LED shows green when the unit is powered. The last position of the switch has a spring-loaded momentary action, and the user has to hold the switch over in this position for at least two seconds to turn the 48V phantom power on, whereupon the power LED turns red. The two purple rotary controls on the left-hand side adjust the microphone or DI input gain for each channel, but there is no provision for stereo linking and there are no visible calibration marks for setting gains accurately or repeatably.

Microphones are connected via the XLR sockets, while the integral TRS sockets accept the output of electric guitars and basses, loading them with a 2.2M(omega) input impedance. The amplifier gain range spans 12-65dB, and the circuitry was developed by the same Apogee team that designed the impressive Trak 2 preamp & A-D converter. If phantom power is switched on it is made available only to the XLR sockets — if a TRS plug is inserted, or the associated gain control is turned back to select the line input mode, then phantom power is disabled on that channel.

Test Spec     • Apogee Mini-Me ASIO driver v2.0.8. • 1GHz Pentium 4 PC with ASUS motherboard and 256MB RAM, running Windows 98SE. • Tested with Syntrillium Cool Edit Pro v2.1 and Steinberg Cubase VST v5.

Line-level inputs are also connected via the combi jack/XLR sockets, but selected by turning the gain controls fully anticlockwise to engage a back-stop switch. The gain is then adjusted using recessed multi-turn screwdriver trimmers, enabling a calibrated line-level input gain to be established anywhere between +10dBu and +4dBu. The factory calibration provides the SMPTE alignment of 0dBu to -20dBFS. Simple headroom bar-graph meters comprise two sets of four LEDs situated between the input gain controls. Red overload LEDs are accompanied by yellow lamps at -2dBFS, and green for -12dBFS and -40dBFS.

A pair of toggle switches are mounted to the right of the second channel's gain control to enable and configure the soft limit and Push-It compressor facilities. The top three-way switch selects off, soft limit and soft limit with compressor, while the bottom three-way switch selects the required compression ratio (curve one, two, or three). The soft limiting has been seen on many other Apogee A-D converters, including my own PSX100, and helps to guard against overloads by progressively increasing the ratio of a high-threshold compressor over the top 4dB or so of the quantiser range. Signals below -4dBFS are completely unaffected, but high-level transient peaks which are at risk of causing overload are instantaneously compressed such that they remain below 0dBFS. The system works extremely well, and many engineers use it deliberately as a creative element during recording, simulating in some ways the saturation effects of magnetic tape recorders.

The Push-It compressor is an extension to the soft-limiter, and does much as its name implies — it introduces a bootstrap compressor to help to lift quieter input signals, while also providing protection against digital overloads. There are three curves, set at the factory to provide varying degrees of compression, although the first curve is essentially a soft-knee limiter with a threshold set to about -10dBFS. Curve two has a ratio of about 1.2:1 and curve three is heavier at around 2:1.

However, curves two and three can be adjusted by the user for slopes anywhere between 1:1 and 3:1. Curve two has the fastest attack and release times (although both are programme adaptive) and is intended for use with percussive signals, while curve three features slower attack and release times and is intended for vocal and instrumental sources.

The third purple control is a 12-way rotary switch used to select the A-D sample rate. For the standard rates of 44.1kHz and 48kHz the user can select any of three different word lengths (16, 20, or 24 bits) by dialling in the appropriate switch position. At the elevated sample rates of 88.2kHz and 96kHz the output is always at 24-bit resolution. The word length reduction is provided by the UV22HR algorithm.

Unusually, four of the twelve positions on the dial don't output any audio at all. These simply output 'digital black' signals at one of the four sample rates (44.1, 48, 88.2 or 96kHz) to enable the Mini-Me to act as a word-clock reference. The intention is to allow the low-jitter clock within the Mini-Me to be used as the clock reference for a DAW, thereby potentially improving the audio quality during playback if the DAW hardware clock is less accurate.

The final two controls comprise a fourth purple dial and a smaller knurled knob. The former sets the monitoring level for the headphone output on the rear panel, while the latter allows the user to monitor either the direct analogue input, the USB return signal, or a mixture of the two. This control can also be pushed to switch between mono and stereo monitoring, allowing a single input to be heard on both earpieces, for example. The headphone amplifier provides up to 300mW per channel (RMS).

While some USB audio interfaces can transfer data with elevated sample rates, the Mini-Me (currently, at least) can't handle audio data at sample rates above 48kHz, partly because of the increased problems with jitter over USB. In practice, I doubt the lack of 96kHz USB interfacing will cause great consternation to many users, and the AES-EBU or S/PDIF outputs from the Mini-Me can always be coupled to the appropriate digital inputs on a suitable interface card at 96kHz, if required, with far better performance.

The USB connector allows direct interface with Windows PC and Apple Macintosh systems, although only at 44.1kHz and 48kHz sample rates.

However, I was left wondering what would happen if I had set the Mini-Me to operate at 96kHz, but still connected the USB interface. It turns out that the output from the A-D converter is routed directly to the AES-EBU and S/PDIF outputs, but that it passes through a sample rate converter en route to the USB port. The output sample rate (and bit depth) is then determined by the software running on the computer and is completely independent of that at the Mini-Me's main digital outputs set by the front-panel controls. Clever, huh?

Apogee strongly recommend connecting the Mini-Me directly to a computer's USB port — not via any kind of USB hub or extension device — and with a cable no longer than 5m, in order to minimise data jitter. Although the Mini-Me will usually work with the computer operating system's standard USB drivers, Apogee strongly recommend using their own ASIO drivers. This is particularly important in the case of the various Windows operating systems, where the Apogee drivers extend the system-wide support to enable the Mini-Me to function correctly even with applications that do not use ASIO.

Unusually, these Apogee drivers are not shipped with the unit (and neither is a suitable USB cable, incidentally). Instead, you have to download the appropriate drivers from the Apogee web site, thus ensuring you start with the latest version — currently v2.0.8 for both Mac and Windows platforms. Registered users of the Mini-Me receive automatic email notifications of new software updates.

The supported operating systems are OS 9.1 and OS X and above for the Mac, and everything from 98SE and above for Windows, although there are, naturally enough, various limitations with the different operating systems. For example, there are some problems with Mac OS 10.2 while the native USB audio support is still being improved, and with early versions of Windows XP. I mainly used the Mini-Me with a Windows 98SE laptop PC without any problems, and the installation program does it's job well. For XP users, there is an excellent and extremely detailed page on the Apogee web site explaining how to optimise XP for audio applications, right down to editing the Registry.

The Mini-Me is simple to set up and use, either as a stand-alone converter or as a USB interface. I mainly used it in its stand-alone mode and was able to compare it with units such as the Apogee PSX100 and the Drawmer DC2476. Its performance is little short of astonishing, given its size, and compares very favourably with those larger units on a line-level input. Clock stability seems to be up to Apogee's usual high standards, and stereo imaging is wide, stable and detailed, suggesting that jitter is, indeed, very low.

The Mini-Me has no word-clock facility (either input or output), so multiple machines cannot be synchronised together for multi-channel work. Clearly, though, the Mini-Me wasn't designed for that kind of application — it is a straightforward, portable two-channel device. The mic amps are quiet and transparent, their Trak 2 heritage showing clearly, and the DI input also worked very well, with a useful gain range. I liked the calibrated line input facility, but it would have been nice to have a stereo link mode for the mic inputs to enable accurate level setting on both channels. The rotary controls seem to be very sensitive as regards level change versus position, and the meters are far too coarse to set levels accurately on the Mini-Me itself. A switch to set both channel gains from one control would have been a very useful feature.

The new Push-It compression facilities are a worthwhile addition, combining the overload protection of the soft limiter with more musically useful compression. Although the adjustment is only through selection of one of the presets, the programme-dependent attack and release times seem to cope well and the preset ratios permit a useful variation in the amount of compression. There is no gain-reduction meter as such, but then this design doesn't really apply gain reduction so much as low-level lift — which is harder to display even if there was sufficient panel space. It's really a case of using your ears to select the most appropriate level of processing and, since the system is virtually impossible to overload, there's nothing to worry about other than the artistic impression.

This is a very high-performance A-D with some very handy additional facilities in a remarkably compact unit. For anyone looking for a portable but very high-quality recording and monitoring system, this is an impressive solution.

information

Mini-Me, £1291; padded carry-case, £45.83. Prices including VAT.  Arbiter Music Technology +44 (0)20 8970 1909.  +44 (0)20 8202 7076.  Click here to email  www.arbitergroup.com  www.apogeedigital.com