The name of this little box of tricks may ring a bell: Cambridge Audio has had a DacMagic in its range before, but the last one disappeared a while ago when DACs appeared to be in terminal decline. Now they are back and the name has been revived for what is, in fact, an all-new product.

A major reason for the resurgence of DACs in general, is the proliferation of digital audio sources, especially computers. Cambridge has catered for this by providing the DacMagic with three inputs, USB, 'traditional' phono and optical S/PDIF.

Compact but well-connected

There are plenty more connectors on the back panel, because Cambridge has also provided a digital output (both flavours), while analogue audio signals appear in both unbalanced and balanced form – a welcome surprise at this price. The last socket is for the external power supply, important in enabling the DacMagic to inhabit such a small case.

Plenty of manufacturers would doubtless be happy enough to be able to offer a completely basic DAC for £200, but Cambridge is on a bit of a roll with its enhanced feature sets.

As a result, we are treated to a version of the deluxe upsampling technology first seen in the 840C and 740C CD players from the Azur range.

Digital filtering

Devised by software specialist Anagram Technologies of Switzerland and licensed – exclusively, to date – to Cambridge, this uses high-power digital signal processing technology to perform the digital filtering function.

In the 740/840 models it upsamples to 384kHz: here, a more modest version upsamples to 192kHz, but adds the flexibility of three filter types: 'linear phase', 'minimum phase' and 'steep'. The differences between these filters are in some ways subtle, but may be significant in determining the DAC's sound.

Linear phase is the type of filter most commonly used in up/oversampling players, since the very first Philips' machines in the early 1980s. It gives no phase shift at all within the audio band and rolls off very sharply around half the sampling frequency.

As most commonly implemented, it has rather limited attenuation at exactly half the sampling frequency and, as a result, allows a little bit of aliasing distortion to occur if there is any audio above 20kHz. There is also pre-ringing on transients, though this has never been shown to be a real problem.

Good quality components

Minimum phase filters do without the pre-ringing, but do have some phase shift in the audio band. The actual frequency response is, to all intents and purposes, identical to that of the linear phase filter. The 'steep' option, meanwhile, is another linear phase filter, but with faster roll-off above 20kHz so that, effectively, no aliasing occurs.

There is slightly more pre-ringing than with the linear phase filter. This needs a little more processing power than the other filter types, but it should theoretically be the best of the lot – except that this one adds a small, but not vanishing amount of passband ripple, something of poorly understood subjective significance.

Whatever the theory says, it's good to be able to choose. The same is true of absolute phase, which can be inverted digitally by the DacMagic. All this wizardry is achieved by a Texas Instruments digital signal processing chip, aided and abetted by DAC chips from Wolfson and some decent op-amps and passive components.