Aardvark Aardverter

Mike Collins investigates the versatile AardVerter — a 16‑bit converter packed with features.

US company Aardvark manufacture a range of useful digital audio boxes which is now available in the UK: it includes the AardScape analogue tape saturation processor, the AardDDA digital audio distribution box, the AardSync II master sync generator — and the AardVerter professional A/D and D/A converter, reviewed here.

The AardVerter has both A/D and D/A converters in one box and is a low‑noise and low‑distortion 16‑bit device with 2‑stage RF filtering. The unit has a naturally dithered output which is optimised for use with 16‑bit workstations — using a very low‑jitter clock — and level meters are provided on the front panel, along with a diagnostics display to check what's coming in and going out and whether it's being clocked correctly. A tone generator is also included, and this generates a full‑scale 0dB tone for setting up levels, along with a silence generator for digital 'black', which you can use to stripe a DAT tape. The latest Delta‑Sigma converters from Crystal (good 16‑bit converters rather than poor
20‑bit converters) and 64x oversampling technology are used; for compatibility with older DAT players, a de‑emphasis filter is automatically applied if the emphasis flag is set in the incoming digital audio signal.

The back panel has balanced +4dBu analogue line in/out, AES/EBU digital in/out and sync — all via XLRs — with a socket to connect the external power adapter. On the front panel, you get rotary controls for the analogue left and right inputs, two rows of LEDs for peak metering, with an associated Hold button, switches for sample rate and sync source, and a mode button to switch the bottom row of LEDs to indicate the sample rate and sync settings. Conveniently located beneath each of the A/D level controls is a pair of tiny recessed trim controls for the analogue input and output levels. A front‑panel On/Off switch and associated Power On indicator are also provided.

Sync'Ing Options

The sample‑rate switch lets you select the sampling rate of the internal clock between the three internal rates available (32kHz, 44.1kHz and 48kHz), while the sync switch also has three positions — Normal, Master and Digital. Normally, the A/D and D/A converters run independently of one another, so the D/A converter clocks from the incoming digital audio signal, whereas the A/D converter is clocked from the internal crystal. The internal clock offers pretty good low‑jitter performance, which helps to eliminate the effects of serial link jitter when other digital devices are connected. To take advantage of this, you can use the Master sync mode, which locks both A/D and D/A converters to the internal crystal. In this case, all external equipment being fed from the digital audio output must be put into slave mode, so that everything is locked in turn to the AardVerter's clock. Alternatively, both the D/A and A/D can be synchronised to the external sync input or the digital audio input, if you want to use an even higher‑quality external master clock source.

To lock to a sync signal coming in via the digital audio input, you switch the sync to Digital on the front panel; if a sync signal is present on the sync input on the back panel, both A/D and D/A will lock to that signal regardless of the settings on the front‑panel sync switch. You can actually lock to sampling rates between 25 and 50kHz when you're using external sources — which you will need to do if you are working with video, for instance, where the sampling rates employed depend on the video frame rates in use.

Inner Secrets

Various jumpers inside the unit let you make custom configurations. You can disable the front‑panel rotary controls for analogue input levels, making the recessed analogue input level trim controls on the front panel active instead — a useful way of preventing inveterate knob‑twiddlers from altering your carefully adjusted levels! You can also set the channel‑status format of the digital output to be either AES/EBU or S/PDIF, and you can adjust the analogue inputs to suit professional balanced or consumer unbalanced voltage levels.

The internal clock offers pretty good low‑jitter performance.

But all the connectors on the back panel are professional balanced XLRs — so how can you connect unbalanced consumer devices? Well, Aardvark have got this covered too. Phono‑to‑XLR and XLR‑to‑phono adapters can be supplied with the unit, so that S/PDIF signals can be routed via the digital input and output sockets, and unbalanced analogue signals can be routed via the analogue inputs and outputs. The special digital audio adapters available from Aardvark will change the impedance of the connection going from S/PDIF to AES, as well as changing the level of the signal when it goes from AES to S/PDIF. Standard adapters can be used with the analogue inputs and outputs, to change between balanced three‑wire and unbalanced two‑wire connectors.

This all adds up to a very cost‑effective solution, allowing the unit to be used with either consumer or professional equipment but keeping size and cost to a minimum.

Operational Aspects

Simply pressing the mode button toggles the AardVerter between Conversion and Smart Diagnostics modes. In its normal Conversion mode, the LED display functions as a dual bargraph display: when an analogue audio signal is applied to the A/D, the LED bargraphs will display peak levels, which are held for half a second. If you want to keep the peaks held indefinitely so that you can check your headroom margin, you just press the Hold button. In Smart Diagnostics mode, the top row of LEDs functions as a peak meter, with left and right channels combined. The LEDs underneath act as status lights, and their functions are, conveniently, described on the front panel below the LED display: they indicate whether input signals are present, what clock sources are being used, which sampling rate is in use and so forth.

To put the unit into the Reference Tone Generation or Digital Silence Generation mode, press and hold the Mode button. If you hold this down for two seconds, the display shows two dots chasing each other clockwise to indicate that you're in the Tone Generation mode: the converter outputs a 1kHz reference tone via both analogue and digital outputs. To produce digitally generated silence at the outputs, press the Mode button again; the dots will chase round anti‑clockwise to indicate that this mode is in operation. When you're finished with all this, another press on the mode button takes you back to Conversion mode.

Using these features, you can prepare your DAT tapes to be sent for mastering just as they do in professional studios, by striping the DAT tape with digital 'black' or silence so that the signal drops to silence between every track you record, and putting a few seconds of 1kHz tone at the beginning of the tape set to the 0dB level you're using in your studio. Playback levels can then be set correctly when the tape's played back in the mastering studio.

Verdict

If you are looking for a versatile set of 16‑bit converters to use with your digital audio workstation, the AardVerter can be configured to suit just about all the scenarios you're likely to encounter. Subjectively, its audio performance is adequate, and the technical features are extremely versatile and well thought‑out. Professional engineers will particularly value the tone‑ and silence‑generation facilities, while home‑studio users will appreciate the ability to interface with consumer equipment.