Altec 8558B
The Altec 8558B is a programmable microaudio equalizer from Altec Lansing's professional audio lineup, likely introduced in the late 1980s. It packs 28 1/3-octave filters, each with 12 dB of cut or boost, into a single rack space. Eight memory presets let the user store and recall different EQ curves. There are no front panel controls at all. That was a deliberate choice, and it set the unit apart from the slider-covered graphic equalizers common at the time. Fixed high-pass and low-pass filters are included. The audio connections are electronically balanced, with a transformer-balanced option available as an accessory.
DB-Magazine (September 1989, p.79) listed the 8558B at $1,198.00, alongside Altec's 1753A and 1750A equalizers. The same publication (September 1991, p.59) repeated the core specifications - eight memories, 28 filters, 12 dB cut/boost, fixed HP/LP filters, electronically balanced in/out with optional transformer - and gave dimensions of 1.75 by 19 by approximately 7 inches.
Beyond these directory entries, the Archive's research has turned up no service literature, user manuals, or application notes.
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