Chapter 17

De-Noising/Audio Restoration (Out, Damned Spot!)

The domain of a Mastering Engineer includes de-noising and audio restoration skills, making an overview important to explore. The common features of modern de-noise plug-ins (or standalone hardware or software onboard your DAW) are algorithms that will: de-buzz, de-click, de-clip, de-crackle, de-hiss, de-hum, perform spectral editing/repair, and provide tools for vinyl restoration (Figure 17.1). These tools allow the Mastering Engineer to identify, isolate, and remove unwanted noise or artifacts and restore audio. The applications of audio restoration include TV/film dialogue, cleaning up multi-track recording channels, and application of master file de-noising. In this chapter, I will explore four options for denoising and audio restoration.

Sonic Solutions NoNoise

The Sonic Solutions NoNoise plug-in suite (for the Macintosh platform) has a long history as an effective audio restoration option. It must be noted that the first commercially embraced de-noising system I can recall was the original Sonic Solutions NoNoise. In the mid-1990s when I began mastering at Capitol (before the proliferation of plug-ins), we were using the hardware/software version of this system. At that time, it was championed and embraced by one of our then senior Mastering Engineers, Bob Norberg. It implemented a three-step methodology which included de-hiss, de-click, and de-crackle algorithms. The de-hiss algorithm used a pure hiss ‘noise estimate’ (ideally from a silent area of your audio file with mostly noise and no or very little audio) to then interpolate and remove that same noise from the entire file in a background DSP process. The user could adjust the intensity of the de-noising with threshold, reduction, and other user parameters. This would achieve some dramatic results on older analog recordings besotted with tape hiss or other artifacts. They would subsequently play back with nearly crystal-clear fidelity. A similar robust and effective de-noising algorithm has evolved into the current Sonic Solutions plug-in format.

Figure 17.1

Figure 17.1The Weiss DNA-1 is a standalone hardware de-noiser that includes a broadband de-noiser, a de-clicker, and a de-crackler. It also has the same K-Stereo ambience recovery algorithm from the UAD plug-in (see Figure 15.9). The output section consists of an additional M/S encoding/decoding matrix for final stereo width shaping.

Source: (courtesy Weiss)

Similarly, the de-click and de-crackle passes would allow for samples of the unwanted noise to be taken and then selected for the specific algorithms to interpolate and remove. Bob discovered that by setting the parameters for a gentle intensity and then running multiple passes, the best results were achieved. Invariably, there was a point where the de-noise algorithm would leave a watery or ‘phasey’ sound on the audio (referred to as artifacts) that was worse than the original. This meant that selecting the best pass was part of the process. But if the parameters were dialed in correctly, the results were often impressive.

Sonic Solutions NoNoise represented a groundbreaking de-noising system and remains a standard in professional mastering. However, as time went on, the zeitgeist shifted, and the belief grew that relevant sonic information was also being removed during the de-noising passes. Additionally, the Sonic Solutions hardware systems fell out of favor because it used a proprietary digital file system (not .wav or .aif) that could only be played back on another Sonic system. Finally, the original Sonic system was limited to standard resolution, and with the proliferation of high-resolution digital audio in the 2000s, it became passé. Sonic later re-tooled the technology to run as it does today on Macintosh-based DAWs. I can recall using the de-hiss function most often on certain introductions and fade-outs of projects from original analog tapes.

Izotope RX7

Izotope RX7 is a modern DAW-hosted de-noise software plug-in that also functions as a standalone application. It has extensive audio repair, learning, and re-balancing options. It also has options to remove various sounds/noises such as 60-cycle line hum, clips, or other audio artifacts in the recording via spectral repair. Quite powerful, it functions with .wav or .aif files in all sampling frequencies and bit depths. I have found that the plug-in de-clipper is excellent at reintroducing dynamics on a peak-limited file, and it also softens the high-frequency extension, making it a viable option for creating MFiT files, files for vinyl cutting, or files for digital streaming that have a lower recommended LUFS level, such as for Spotify (Figure 17.2).

Figure 17.2

Figure 17.2The iZotope de-clipper can eliminate inter-sample peaks, reintroduce dynamics on a peak-limited file, and soften high-frequency extension, making it a viable option for creating ADM (formerly MFiT) files.

Source: (courtesy iZotope)


Cedar is another company that manufactures audio restoration devices (both real-time hardware and software plug-in versions). Applications include removing unwanted artifacts (surface noises, hiss, and other analog artifacts) from digital files, as well as real-time de-noising of analog tape, vinyl album, or transcription disc during transfer to digital. At one point in the late 1990s, I worked with a renowned engineer originally employed at Abbey Road Studios in London named Malcolm Addey. Malcolm had worked on a number of Beatles sessions in the early 1960s, and possessed an upbeat and jovial personality, along with a characteristically British self-possessed demeanor. He was accomplished and great fun to work with. We were transferring Count Basie recordings from the 1930s and 1940s from transcription discs in an era of recording when they would record a band or orchestra directly to a lathe. These recordings sounded wonderful with incredible purity and vitality, likely due to the simple microphone-to-lathe recording path and discrete electronics incorporating tubes and transformers in between. I would spray the transcription discs with Formula 409 Cleaner (a method for quiet transcription disc transfers that I gleaned from another senior engineer at Capitol, Jay Rannellucci) for the transfer, then very carefully rinse them in a large tub, and rack dry them. In addition to the Formula 409 Cleaner, Malcolm brought in a Cedar de-noise device that would remove additional hiss and pops. It literally had one threshold knob to control the intensity of the noise removal, but it worked perfectly. Cedar is still known for designing quality audio restoration hardware and software.

Options Onboard Your DAW

In DAWs designed for mastering applications, there are usually some basic de-noise functions available. I regularly use Steinberg WaveLab as my RDAW for mastering and it has a waveform restorer function that is excellent at removing tics, pops, and other noises that can be seen (and heard) in the waveform (Figure 17.3).

Figure 17.3

Figure 17.3Before and after screen captures of an impulsive ‘tic’ in highlighted region removed by WaveLab’s onboard waveform restorer algorithm.


De-noising and audio restoration experience remains relevant to a Mastering Engineer’s skill set. Every mastering studio should have one of the common de-noise options available to handle any restoration issues that may arise. Common options are Izotope RX7, Accusonus ERA Bundle Pro, Antares SoundSoap+ 5, Cedar Audio Studio Complete, Sonnox Restore Collection, and Waves Audio Restoration Bundle.


  1. Broadband de-noise a problematic track with excessive tape hiss using Izotope RX7.
  2. Using the Izotope de-clipper plug-in, reintroduce the dynamics to a loudness-maximized track (around +13dBu), creating a file that is +10dBu.
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