I recently acquired an Apogee Duet firewire audio interface.  Of course, Duet 2 became available only a month before my Duet package arrived.  This is fine by me.  I payed very little for the Duet and I am completely content with any Apogee product, even if it does not use USB 2.0 connectivity or a sampling frequency that extends upwards of 192kHz.  Firewire 400 and and a top sampling frequency of 96kHz works perfectly well for me.  In fact, this interface has significantly improved the quality of my recorded sounds and listening experiences.  Before I say more about this, here are a few “features & specifications” for the Duet:

- Two channels of professional-quality 24-bit/96kHz audio input and output
- Two balanced XLR inputs, with selectable 48V phantom power on each input – Maximum input – +4 dBu setting: 20 dBu; -10 dBV setting: +8 dBV
- Mic Pre-amp gain: 10 to 75 dB
- Two unbalanced high impedance instrument inputs
- One high-level stereo headphone output
- Two unbalanced -10 dBV line outputs for powered speakers
- Multi-function controller knob for volume and input gain control and assignable MIDI control
- Multi-segment LED meters to display input or output levels
- FireWire 400, compatible with Mac OS X Core Audio
- Integration and control with Apple’s GarageBand, Logic Pro, Logic Express
and Final Cut Studio (Soundtrack Pro)
- Compatible with any Core Audio-compliant audio application
- Apogee’s Maestro software for advanced control and low latency mixing

In general, I would describe the sonic contributions from the Duet as “full,” painstakingly representing sonic detail with great breadth and depth throughout the 20 – 20kHz audible bandwidth.  With that said, one might begin to wonder how remarkable this claim might be, given how many other audio interfaces claim to offer the same details within the same bandwidth.  Admittedly, I used to overlook the quality of analog to digital or digital to analog (A/D and D/A) conversion capabilities within audio interfaces.  I assumed that my Digidesign interfaces were just fine and that all I had to do was put more consideration into the transducers that I would decide to use.  However, choosing the best microphone or loudspeaker alone does not entirely determine the quality of an audio reproduction.  High quality digital audio recording demands that we also seek desirable A/D and D/A converters.  ‘Nyquistian’ sample rates, as impressive as they might seem, do not guarantee the effectiveness of a converter.  At least two other factors determine the prowess of the A/D and D/A converters within audio interfaces: the clock and dither.

A/D and D/A conversions, in most audio interfaces like the Duet, utilize a pulse code modulation (PCM) system.  Thanks to Charles Nyquist and other scientists who implemented his theorem, the PCM sample rate must be twice that of the frequency bandwidth of the analog audio signal.  In the case of an A/D conversion, the clock generates the sample frequency for flowing binary codes that will quantitatively represent the frequency and amplitude dimensions of the analog input.  Dither is a noise that a PCM system applies to an incoming analog signal in preparation for the moment of conversion.  The complexity of this noise determines how well the converter can represent the details of an analog version in a converted digitized version.  How consistent and reliable this clock outputs this digital ‘pre-data’ that will represent the analog signal primarily determines the success of the converter.  A customized dither that anticipates and counters the imperfections the latter stages within the PCM converter, adding noise energies to the analog input signal in order for listeners to better recognize features in the digital representation also determines the success of the converter.

Apogee prides themselves for the proprietary dither and C777 clocks in their interfaces such as the Duet.  This combination has been the basis for the accumulation of a large number of engineers and musicians who use Apogee products.  While I have split the glory of this type of equipment as coming from both dithers and clocks, I now must conclude that the clock more singularly undergirds the triumphs of interfaces and their converters.

There seems to be something very human about clocks like the C777, as if it shows up to a job on time like a good and reliable worker…