Once properly configured the DacMagic Plus performed perfectly throughout the review period. But the DacMagic does have one ergonomic quirk: its volume control. Unlike most volume controls, which are in some way directly connected to an attenuator, the DacMagic Plus control is more like a switch. When you turn it, it feels loose and sloppy before it engages. Once engaged, it takes a moment for the volume knob to respond. To some prospective users this volume control will feel cheap. But the reason the volume control feels the way it does is because it isn’t an analog or bit-reduction digital controller but a DSP driven digital domain gain stage using Anagram Q5 adaptive time filtering to accomplish gain reduction bit-reduction.
With no dots, numbers, or indicators to tell a user what the relative volume level is, doing repeatable, matched-level comparisons between inputs with different levels was nearly impossible. Some potential users will not care for the volume knob’s feel and lack of level calibration, but for normal everyday use I didn’t find they were a serious issue.
The DacMagic Plus offers three different digital filter settings that can be changed via a front panel button: linear phase filtering, minimum phase filtering, and steep filtering. According to Cambridge Audio, “The Linear Phase filter is a highly regarded audio filter offering low ripple in both the pass and stop bands, and what is known as constant group delay. Constant group delay means that audio signals of all frequencies are always delayed by the same amount when passing through the filter. All audio is therefore fully time-coherent at the output. The trade-off with this type of filter is that due to internal feed-forward in the DSP, its impulse response will exhibit some pre-ringing.” The minimum phase filter “offers even lower ripple in the pass and stop bands. Unlike the Linear Phase filter, group delay is not constant so some time coherence is lost; however, phase shift is low and the particular benefit with this filter is that the impulse response exhibits no pre-ringing.” Finally the Steep filter “is a linear phase filter that has been optimized for stop band attenuation of close-in aliasing images. Here we have traded a little attenuation of the very highest frequency response (-2dB at 20kHz) and a little more pre- and post-ringing for a very steep attenuation just outside the pass band. The Steep filter is able to attenuate aliasing at 22kHz by some 80dB.” Cambridge Audio encourages users to experiment to hear which filter setting sounds best with different material. Each input can have a different filter setting so when a given input is selected a particular filter will be employed.