Introduced in 1998, the Apogee PSX-100 marked a significant development in the company’s range of professional digital audio converters. Building upon Apogee’s established expertise in digital conversion and clocking technology, the Apogee PSX-100 was the company’s first high-resolution conversion system capable of operating at 24-bit resolution and sampling rates up to 96kHz. Its introduction coincided with the recording industry’s transition towards higher-resolution digital recording, DVD-Audio production and 24-bit digital mastering.
Unlike conventional stereo converters designed to perform a single conversion function, the Apogee PSX-100 incorporated two fully independent conversion sections within a single rackmount enclosure. The analogue-to-digital and digital-to-analogue converters could operate separately, use different clock sources or be interconnected through the unit’s internal digital routing system. This flexibility allowed the Apogee PSX-100 to function as a recording front end, monitoring converter, digital format converter or signal distribution system.
The A/D section employed true 24-bit conversion with support for 44.1, 48, 88.2 and 96kHz sampling rates. Apogee specified an unweighted dynamic range of 116dB and an A-weighted figure of 119dB, together with low distortion and exceptionally accurate frequency response. The converter’s analogue input circuitry incorporated Apogee’s active self-balancing design, accommodating balanced and unbalanced signals while maintaining consistent operating characteristics.
Professional and consumer operating levels could be selected independently, with additional analogue level adjustment provided for calibration. The maximum input level reached +27dBu in professional balanced mode, while separate settings accommodated professional unbalanced and consumer-level equipment. This allowed the Apogee PSX-100 to integrate with a broad range of mixing consoles, analogue processors and recording equipment.
The D/A section used a 24-bit delta-sigma conversion system with an unweighted dynamic range of 112dB and channel separation exceeding 120dB. Its analogue outputs were capable of delivering signals up to +28dBu, providing sufficient headroom for professional monitoring systems and analogue signal chains. Apogee specified a frequency response variation of just ±0.15dB between 10Hz and 20kHz, reflecting the attention given to conversion accuracy.
One of the Apogee PSX-100’s principal features was its comprehensive selection of digital audio interfaces. The unit incorporated AES/EBU, S/PDIF coaxial, S/PDIF optical, ADAT optical and Tascam TDIF connections, allowing it to communicate with a wide range of digital recorders, mixing consoles and computer-based recording systems.
Two AES/EBU input and output connections were provided, with both interfaces used during 88.2 and 96kHz operation. At conventional sampling rates, the interfaces could operate independently. An additional AES/EBU auxiliary output supplied a full-resolution signal, enabling a 24-bit recording to be made while the main outputs simultaneously delivered 16-bit or 20-bit signals processed through UV22HR.
Apogee’s UV22HR processing was an enhanced version of the company’s established UV22 word-length reduction technology. Developed for transferring high-resolution digital audio into lower-resolution formats, UV22HR allowed 24-bit signals to be reduced to 20-bit or 16-bit word lengths. This was particularly relevant for CD mastering, where recordings produced at 24-bit resolution ultimately needed to be delivered in the 16-bit CD format.
The Apogee PSX-100 allowed UV22HR processing to be applied to either the A/D or D/A signal path, depending upon the selected configuration. The system also provided a dedicated full-resolution auxiliary output, allowing engineers to retain an unprocessed 24-bit version of a recording while generating lower-resolution masters. UV22HR processing was available at conventional sampling rates but was not supported during 88.2 or 96kHz operation.
A further proprietary feature was Apogee Soft Limit, designed to increase the usable recording level before digital clipping occurred. By controlling signal peaks approaching full scale, Soft Limit enabled recording engineers to capture higher average signal levels without generating conventional digital overloads. The function was particularly useful when recording programme material with unpredictable transient peaks.
The Apogee PSX-100 also incorporated Apogee Bit-Splitting, commonly abbreviated ABS. This technology allowed high-resolution digital audio to be recorded on existing 16-bit digital multitrack machines by dividing the information across multiple recording tracks.
At conventional sampling rates, a 24-bit stereo signal could be distributed across pairs of 16-bit tracks using the PaqRat format. The resulting data could later be recombined by the PSX-100 to reconstruct the original high-resolution signal.
The enhanced ABS-96 mode extended this capability to 88.2 and 96kHz recording. This allowed a conventional eight-track, 16-bit digital recorder operating at 44.1 or 48kHz to store a high-resolution stereo signal sampled at twice its normal rate. The feature enabled studios equipped with ADAT or TDIF-compatible digital multitrack recorders to undertake high-resolution recording without replacing their existing recording machines.
Three principal operating modes determined how the A/D and D/A converters interacted with the internal routing system.
In Confidence Monitor mode, the A/D and D/A sections operated as independent converters. The analogue input signal was converted and made available at the digital outputs, while the D/A converter could monitor a separately selected digital input. Each conversion section could use its own clock reference, and the two sections could operate at different sampling rates. This mode was particularly useful when recording digitally while monitoring playback from a separate digital source.
Digital Copy mode routed the selected digital input to all available digital outputs and the analogue outputs. Both conversion clocks were synchronised to the incoming digital signal, allowing the Apogee PSX-100 to function as a digital format converter and distribution system. This configuration was suitable for transferring material between digital devices, creating multiple digital copies or introducing UV22HR processing into an existing digital signal path.
In Analog Monitor mode, the signal from the A/D converter was routed directly to the D/A section as well as the digital outputs. This allowed monitoring of the signal after analogue-to-digital conversion, providing a means of checking the converter’s output without requiring an external digital recording or monitoring device.
Clocking accuracy was a central element of the Apogee PSX-100’s design. The unit incorporated two proprietary Apogee low-jitter clock systems, allowing the A/D and D/A sections to operate independently or in synchronisation. The internal crystal oscillators could provide the master reference, while external synchronisation was available through digital audio inputs and word clock connections.
An optional video synchronisation module allowed the converter to lock to NTSC or PAL video reference signals, extending its usefulness to audio post-production and video-related recording applications. The word clock output could be configured to follow the selected sampling rate or provide a conventional 44.1 or 48kHz reference during high-sampling-rate operation.
The front panel provided direct access to the unit’s extensive functions without requiring a menu-driven interface. Large silver push-buttons controlled synchronisation, digital output resolution, optical output format, Soft Limit, Bit-Splitting, metering and digital input selection. LED indicators displayed the selected operating modes, clock status and routing configuration.
Two vertical LED bargraph meters provided visual monitoring of the stereo signal levels. These could be switched between the A/D and D/A sections, allowing the engineer to monitor either conversion path when the two sections were processing different signals.
The metering system included adjustable digital overload detection, with the user able to define an overload as between one and four consecutive full-scale digital samples. Overload indicators could be configured for a two-second hold or an infinite hold, while a dedicated calibration mode provided metering accuracy within ±0.1dB.
Individual left and right channel muting was also provided, allowing either side of the stereo signal to be disabled directly from the front panel. Additional configuration options were available through a ten-position DIP switch on the rear panel, including analogue operating levels, XLR signal polarity conventions, overload indication behaviour and Bit-Splitting settings.
Physically, the Apogee PSX-100 followed the styling of the company’s AD-8000 multichannel converter. Its distinctive purple front panel was inset into a solid aluminium extrusion, with silver controls and illuminated status indicators providing a recognisable visual identity.
The internal power supply employed a toroidal transformer with linear regulation and smoothing circuitry designed to minimise electrical interference and power supply noise. An external heat sink provided thermal management, while internally selectable mains voltage settings accommodated different international power systems.
With its combination of high-resolution conversion, independent A/D and D/A operation, extensive digital interfacing and proprietary processing technologies, the Apogee PSX-100 was designed to bridge conventional 16-bit digital recording systems and the emerging generation of 24-bit, 96kHz production equipment. Its ability to record high-resolution material using existing digital multitrack machines was especially relevant during the late 1990s, when many professional studios were transitioning towards higher-resolution digital production.
The Apogee PSX-100 represents an important stage in Apogee’s development of integrated digital conversion systems, combining precision analogue circuitry, low-jitter clocking and digital signal management within a single professional studio processor.
Features
- Two independent 24-bit analogue-to-digital and digital-to-analogue conversion channels
- Selectable 44.1, 48, 88.2 and 96kHz sampling rates
- Comprehensive AES/EBU, ADAT, TDIF and coaxial/optical S/PDIF digital interfaces
- Apogee UV22HR word-length reduction for converting 24-bit audio to 20-bit or 16-bit formats
- Apogee Soft Limit processing for controlling transient peaks before digital overload
- Apogee Bit-Splitting technology for recording 24-bit and high-sampling-rate audio on conventional 16-bit multitrack recorders
- Three operating modes: Confidence Monitor, Digital Copy and Analog Monitor
- Two independent Apogee low-jitter clock systems with external word clock synchronisation
- Advanced stereo LED metering with selectable A/D and D/A monitoring and adjustable overload detection
- Professional balanced analogue I/O, independent channel muting and configurable operating levels