User manual IZOTOPE IZOTOPE RX RESTORATION GUIDE

[. . . ] Restoring Audio with iZotope RXTM iZotope with Nat Johnson Tools, tips and techniques. © 2008 iZotope, Inc. iZotope and iZotope RX are either registered trademarks or trademarks of iZotope, Inc. in the United States and/or other countries. Other product or company names mentioned herein may be the trademarks of their respective owners. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Intended Audience for This Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] This allows RX to use softer suppression where noise is subjectively inaudible to the human ear. The position of the slider controls the influence of psychoacoustic model on suppression levels. Harmonic enhancement This control allows for softer suppression of harmonics of the signal that could be buried in noise. It can make the resulting signal brighter and more natural sounding, but high values of harmonic enhancement can result in highfrequency noise being modulated by the signal so use it sparingly. Restoring Audio with iZotope RXTM Page 30 of 74 ©2008 iZotope, Inc. HUM AND TONAL NOISE Hum can originate from bad ground connections or inducted from power sources such as AC mains or transformers and can usually be heard audibly as a low frequency tone, usually based at either 50Hz or 60Hz. Hum be easily eliminated using the RX Hum Removal module, which we'll describe in this chapter. Tonal Noise such as buzz from fluorescent lighting, is not as easy to trace back to a primary frequency and may extend up into high frequencies that are out of the scope of what RX's Hum Removal module can handle. Tonal noise varies from broadband noise in that it tends to be concentrated at certain frequencies. We'll also discuss removing tonal noise with RX Denoiser in this chapter. Finding the Hum's Primary Frequency To begin, select a section of the recording where the hum is prominent. Sometimes there will be silence (or near silence) at the beginning or end of the program material that will contain noise but not any other audio. Otherwise, try choosing a quiet passage of the recording where hum is obvious. Next, select the section of audio where the hum is most clearly audible. This will allow you to set Hum Removal's parameters as audio plays back. When attempting to remove hum, you first need to find the hum's primary frequency. The two most common base frequencies for hum are 50 Hz (Europe) and 60 Hz (U. S. ) due to those regions' difference in electrical delivery. It's a good idea to try the 50 and 60 Hz presets included with RX first. If you hear the hum disappear or get much quieter, you'll know you're on the right track. In some cases, for example a recording made from analog tape that is not precisely at its original recorded speed, you may need to choose the "Free" Frequency Type. Selecting this option unlocks the Base Frequency control and allows you to manually find the Hum's root note. With Preview engaged, move the slider up and down until you find the point where the hum lessens or disappears. Using the Spectrogram For even more precise settings in free mode, use RX's Spectrogram Display to zoom in on the project's low frequencies. [. . . ] Try to retain the musical character of the performance while removing as much of the offending noise as possible The recording before running Automatic Declicker Restoring Audio with iZotope RXTM Page 67 of 74 ©2008 iZotope, Inc. Clicks (vertical lines) are now completely repaired Restoring Audio with iZotope RXTM Page 68 of 74 ©2008 iZotope, Inc. Example 6: Removing Clipping from a Phone Interview DETAILS: This phone interview for an iZotope Podcast with producer Morgan Page was recorded with phone line breakout box and USB audio interface. COMMENTS: This is a classic example of input gain being set too high resulting in nasty clipping. In this example the distorted sections can be clearly heard, but looking at them with the Spectrogram Display and Waveform overlay shows them even more clearly. Begin by selecting a section of clipped audio then hitting Compute below Declipper's Histogram Display. [. . . ]