Outboard DACs

Not only does iFi Audio offer solid-state (J-FET) and GE5670-based tube output options but it also includes five different digital filter ‘recipes’ as part of its custom upsampling regime. ‘Bit Perfect’ and ‘Bit Perfect+’ are essentially no filter at all (NOS), the latter operating up to 96kHz only. Both are free of any pre/post ringing artefacts and thus free of time domain distortions [top inset Graph] but neither do they offer any suppression of digital aliasing products immediately outside of the audioband. These, in turn, may deliver significant intermodulation distortion within the audio range. The standard ‘Bit Perfect’ setting has a –0.9dB/10kHz to –3dB/20kHz treble roll-off with CD/48kHz media that’s addressed by the ‘+’ version courtesy of a +0.25dB treble lift at 10kHz, reducing the 20kHz droop to just –0.5dB. Both are better suited to 96kHz media files. The ‘Transient Aligned’ filter is a standard linear phase type that offers an adequate 58dB stopband rejection and exceptionally flat ±0.02dB response (20Hz-20kHz), albeit with some ringing. The ‘Apodising’ and ‘Minimum Phase’ types are free of pre-ringing, though the former incurs substantive post-ringing [bottom Graph] while offering superior digital alias rejection. PM