Digital Phono Equalization using the iZotope RX and Ozone Equalization Modules.

Phono playback equalization for archival disc sources has traditionally been accomplished with an analog phono preamplifier, ahead of digitization. Such preamplifiers normally have variable, separately adjustable settings for the bass and treble portions of phono playback equalization curves. In recent years there has been increasing interest in making digital transfers from disc sources using a flat phono preamp, applying phono equalization in the digital domain using equalization modules included with digital editing and restoration software. To accomplish phono equalization properly in the digital domain, it is essential to apply both frequency and phase responses that are complements of the recording curves. Some older software-based equalization programs failed to provide correct phase response. One popular and affordable restoration program has numerous pre-defined curves identified only by record label, with no information on the turnover frequencies used for those curves, and no provision for separate bass and treble settings. iZotope's popular RX restoration software and Ozone mastering plug-in have analog filter emulations based on Infinite Impulse Response (IIR) minimum-phase digital filters.1 They precisely duplicate both the frequency and phase responses of analog filters, making them ideal platforms for phono equalization in the digital domain. Appropriate filter parameters make it possible to create extremely precise, independently adjustable bass and treble phono equalization curves. This article will describe proper procedures for determining the correct filter settings for the iZotope programs, which will allow the user to create custom curves for nearly any desired playback equalization characteristics. Correct settings for an assortment of phono equalization curves for vintage records will be offered, along with measurements that verify both frequency and phase accuracy. [ABSTRACT FROM AUTHOR]