The equaliser may be usefully cascaded with other processes. For example, the Play Trim feature which appeared on high-end cassette decks was an HF cut/boost equaliser which preceded the noise-reduction stage. By selecting the Stereo Lab equaliser prior to the Cassette Noise Reduction, Play Trim functionality may be accomplished (see below).
Similarly, the Stereo Lab Equaliser may be usefully cascaded with the Cassette NR process to compensate for the over-bright sound of Type II, III and IV tapes when replayed with the standard (IEC Type I), 120µS equalisation. Just select -4dB HF cut.
The Stereo Lab Equaliser is based on a pair of the famous Pultec EQH-2 equalisers; a combination often found in mastering studios. Control for the equaliser is on its own separate Preferences tab. As with its hardware forebear, software control offers simultaneous boost and cut. The equaliser may be used in Left/Right (L /R) or Sum/Difference (Σ /Δ) mode. There is a check-box to activate sum/difference mode. This mode is very useful for archival or restoration work with stereo phonograph discs.
The tube gain-make-up amplifier is optionally emulated too. There is an option check-box labelled tube-gain. With this checked, the makeup gain contains the (euphonious) distortions associated with a tube circuit with input- and output-transformers. The circuit of the EQH-2 tube make-up amplifier is given below. When the check-box is un-checked, the make-up gain applied is entirely "clean" and has no character of its own.
For the moment, the equaliser only emulates the Pultec EQH-2 for the bass controls set at 30Hz and the treble controls set at 10kHz. This is the most general, useful setting and has been modelled first. To quote from the original Pultec manual for the EQH-2,
TO ADD THAT "FINAL TOUCH" TO THE BALANCE OF GOOD PROGRAM MATERIAL, AND TO GREATLY....
IMPROVE THE QUALITY OF PROGRAM MATERIAL PREVIOUSLY RECORDED ON EQUIPMENT OF INFERIOR QUALITY OR DIFFERING CHARACTERISTICS.
It is usually those tones on the extreme ends of the musical spectrum which lose their proper perspective in the many steps between the musician and the ultimate listener. The wide range of equalization curves provided in the Model EQH makes it possible to correct the very low and very high frequency notes of the orchestra without "muddying up" the middle register instruments.
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