Focusrite ISA-131
The dual-channel dynamics module that anchored Focusrite's ISA line for stereo work. It is the ISA 130 doubled up and linked, with the same performance specs and one thing the mono original never had.
Overview
The ISA 131 is a dynamics processor module. The simplest way to describe it is as a dual-channel version of Focusrite's ISA 130. According to a Recording Engineer product notice, it shares the ISA 130's performance specifications and gives you two channels of compression/limiting and noise gating. It also adds a Stereo Link facility, which the single-channel original did not carry. If you were building a console or a rack around Focusrite's modular ISA architecture, the 130 handled one channel and the 131 handled two, and you could tie them together for stereo work.
The module first showed up at a trade show. Studio Sound (March 1989, p.19) reported that the ISA 131 was shown for the first time at that exhibition. It was described as a dual-channel version of the ISA 130 with the same specifications, and it sat alongside the existing ISA 110 and ISA 115 input signal amplifiers, the remote-controlled ISA 116 mic preamp, the ISA dynamics processor, and channel strips from the Forte series of consoles. So the 131 was the newest member of a modular family that already had the 110 on the preamp/EQ side and the 130 on the dynamics side. The 131 was the stereo-linked extension of the dynamics half.
Focusrite's own advertising of the period laid out the intent behind the ISA dynamics line. It ran in Studio Sound (December 1989, p.39) and Mix (February 1990, p.68). The copy claimed a Focusrite dynamics processor "gives more control and sounds better than anything else you can buy". That is marketing, and should be read as such. The same advertising called the noise gate/expander "extraordinarily fast and sensitive" while still musical enough to handle unwanted sibilance and, in the company's phrase, to "breathe personality" onto even the most recalcitrant vocals. So the gate was pitched as a tone tool rather than a plain noise-muting utility.
Mix (October 1989, p.282) carried a new-products notice on the ISA 131 that fills in the practical side. The unit included an integral power supply — meaning it could stand as a rack piece rather than a bare card needing external power — and it was described as electrically identical to the ISA 130 already respected by many users. The notice also noted the Stereo Link facility, which allowed one ISA 131 to combine with another ISA 131. That's the detail that matters for anyone planning a system: the 131 wasn't just two channels in one box, it was designed to pair with a second unit for larger linked configurations. The same notice referenced a full security lock-out system and an EQ curve comparison function with a true EQ curve display, though those features read as part of the broader product announcement and should be treated cautiously as 131-specific claims.
The module has a documented working life outside the spec sheet. A Studio Sound (May 1994, p.52) equipment list from Le Studio Mobile, a mobile recording operation, names the Focusrite ISA 131 alongside an ISA 215 among the outboard in its rig. The same piece quotes the team praising the Focusrite units as "superb" and notes extensive use of outboard preamps and equalisers. That is a working mobile studio, not a brochure, so the 131 was trusted on location sessions. An EQ (December 1992, p.63) tour report also lists Focusrite ISA-131s among an array of compressor/limiters on the road, alongside Drawmer 1960s and DL 231s and BSS models.
By the late 1990s the 131 was a secondhand item with a known price. A Studio Sound (January 1999, p.?) classified listing offered a "Focusrite ISA 131 - 1U dynamics package" at £1,395. The "1U" part matters: the module was a single-rack-unit package, a compact footprint for two channels of dynamics with an integral supply. The price is a used-market figure from the period, not an original list price. It shows what a working example commanded near the end of the decade, not what it cost at launch.
For collectors, the ISA 131 is the stereo-linked sibling of the ISA 130. It shares that module's performance specifications, adds the Stereo Link facility, and belongs to the same modular ISA family that produced the ISA 110 preamp/EQ and the ISA 115. It is not the ISA 110. The 110 is the module that made the Focusrite name and got reissued. The 131 is the dynamics half of the system, the piece you'd pair with preamps rather than the preamp itself. Buyers hunting the ISA line should keep the distinction straight: the 130 is the mono building block, the 131 is the dual-channel version with stereo linking, and a second 131 can be combined with the first via that link facility. The integral power supply makes a single 131 a self-contained rack unit, which is friendlier than a bare module needing a host frame.
The record does not give a full specification sheet. No frequency response, no gain range, no attack/release figures, no dimensions or weight appear in the available documentation for the 131 specifically. The detailed dynamics numbers that circulate for the ISA line belong to sibling modules and should not be attributed here. What is confirmed is the architecture: two channels of compression/limiting and noise gating, shared performance specs with the ISA 130, a Stereo Link facility, an integral power supply, and a 1U rack format.
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