Apogee PSX-100
A two-channel 24-bit/96 kHz converter that became the reference point for project studios that didn't want their converters to be the weak link.
Overview
The PSX-100 is a two-channel A/D and D/A converter - 24-bit, with sampling rates of 44.1, 48, 88.2, and 96 kHz. The first thing collectors mention is that each converter has its own clock, so the A/D and D/A sections run independently of one another. That one design decision opens up the operating modes that define the unit: Confidence Monitor, Analog Monitor, and Digital Copy. In Confidence Monitor mode the A/D doesn't feed the D/A directly. Each side uses its own low-jitter clock, so the converter can be treated as two separate boxes, even running at different sampling rates.
The input and output stages are unusually complete for a two-channel box. Analog I/O is on XLR, and the back panel carries two AES/EBU inputs and three AES/EBU outputs, plus coaxial S/PDIF, optical (selectable between ADAT and S/PDIF), and TDIF, along with word-clock in and out. The unit is 1U high and 14.25 inches deep, weighing in at 12.5 lbs. Frequency response is quoted at 10 Hz–20 kHz (±0.025 dB), THD+N at -112 dB (A-weighted), and dynamic range at 119 dB (A-weighted). Those numbers are the kind that get repeated in studio corridors, and they hold up: this is a converter that was built to get out of the way rather than to add a sound.
What sets the PSX-100 apart from a plain converter is that it also does real-time format conversion. It can send an analog signal through the A/D to a digital output while converting a digital input to analog through the D/A at the same time. That routing flexibility made it a hub in small studios juggling DAT, ADAT, CD-R, and hard-disk recorders. All of the digital outputs run at once, so a single source can feed several destinations without repatching. And because a 24-bit signal is always available from the AES/EBU aux output, the unit can deliver two different resolutions simultaneously - a 24-bit/44.1 kHz feed to a 24-bit DAT machine alongside a 16-bit backup to a CD recorder.
The word-length story is where Apogee's house technology comes in. Both converters begin by turning analog into a 24-bit word. To get to 16- or 20-bit output, the user selects UV22 via the Output Res button. UV22 is Apogee's take on dither and noise shaping. It places a high-frequency clump of energy around 22 kHz that acts as a bias, pushing the noise floor down toward the theoretical 16-bit level so that quiet sounds fade smoothly into the noise rather than truncating harshly. It's transparent and gives 16-bit recordings at 44.1 or 48 kHz a clarity that surprises people who expect 16-bit to sound like a compromise. Apogee itself warns about one caveat: because UV22 lives around 22 kHz, material destined for downward pitch shifting or aggressive data compression is better recorded without it, since those processes can expose the added energy. And UV22 is unavailable at the faster 88.2 and 96 kHz rates.
For high-resolution work on modular digital multitracks, the PSX-100 uses Apogee Bit Splitting (ABS 96). It spreads a two-channel high-resolution signal across all eight tracks of an MDM, combining bit-splitting and sample-splitting so that 24-bit/96 kHz audio can live on an 8-channel, 16-bit recorder. Mix (November 1999, p.136) covered the unit's ability to mix to a 24-bit device while taking advantage of UV22. Playback of ABS 96 material requires the PSX-100's D/A for decoding. The Rosetta, being A/D only, can't monitor it at full resolution. The S/PDIF outputs can be used for monitoring by sending every other sample to the D/A, which yields 44.1 kHz at the 88.2 rate and 48 kHz at 96 kHz. Without the proper filters, though, that audio isn't suitable for recording because of aliasing and other artifacts. The PSX-100's aux output behaves similarly when monitoring.
The front panel is dense but logical. Buttons cover output resolution, Soft Limit, optical output format, A/D Sync for selecting the sync source, individual channel mutes, ABS and Digital Copy mode selection, an A/D or D/A metering selector, and an MDM Input selector for choosing which tracks to monitor. Most buttons do double duty. A quick press gives the printed function, and a two-second hold reaches a second layer of parameters. Holding Output Res during power-up returns the unit to defaults (DIP switches excluded). Holding A/D Sync enters Fast mode for 88.2 and 96 kHz operation. Back-panel DIP switches handle the set-and-forget configuration - input and output levels independently selectable between -10 and +4 dBu, and the number of consecutive full-scale samples (1 to 4) required before the meters flag an over. Reviewers found the press-and-hold scheme easy to memorize.
Soft Limit is Apogee's proprietary subtle compressor/limiter. It engages as the source approaches the digital ceiling of 0 dBFS, avoiding overs so the engineer can record a hotter signal. One reviewer found it invaluable on an organ with an extreme dynamic range, and useful for mixing and mastering as well as direct-to-DAT field recording. The PSX-100 carries a vertical LED bar-graph meter per channel with an overload light, plus adjustable trim controls for setting the level into the A/D. Some users preferred the Rosetta's longer horizontal meters for visual feedback, but the PSX-100's shorter vertical pair gets the job done.
Apogee's own advertising billed the PSX-100 as a two-channel 24/96 A/D and D/A with AES, TDIF, S/PDIF, and ADAT interfacing, 44.1-96 kHz sampling, and built-in 96 kHz bit-splitting. Audio (January 2000, p.25) noted that the design derived from Apogee's professional studio converters and was intended for the home studio, with a 24-bit signal path capable of preserving the source. The unit was positioned below the flagship eight-channel AD-8000 but used similar converter technology. That was the comparison that mattered to buyers: the AD-8000's sound and 88.2/96 kHz capability, without paying for eight channels.
Collectors and working engineers note that the PSX-100 occupies an odd but fond place in the market. It's a professional-grade converter from the era when outboard conversion was a genuine upgrade over what came built into interfaces, and its format-conversion and simultaneous multi-resolution outputs keep it useful in rooms that still run legacy digital gear. The DIP-switch configuration and press-and-hold button layers are the usual friction points for new owners, and this is not a plug-and-play box. The UV22 restriction at high sample rates is a real limitation for anyone doing pitch-shifted sound design. The independent clocks, the 24-bit signal path, and a transparent Soft Limit are why the PSX-100 still turns up in studios that could afford to replace it and haven't.
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