Spectral De-noise - RX 8 Help

May 2024 · 12 minute read

STD & ADV Module & Plug-in

Table of Contents

Overview

Spectral De-noise is designed to remove stationary or slowly changing tonal noise and broadband hiss by learning a profile of the offending noise and then subtracting it from the signal. It can be useful for tape hiss, HVAC systems, outdoor environments, line noise, ground loops, camera motors, fans, wind, and complex buzz with many harmonics.

Spectral De-noise learns a profile of the background noise, then subtracts that noise when a signal’s amplitude drops below the specified threshold. It is a flexible tool that can be used to quickly achieve accurate, high-quality noise reduction. It also provides separate controls for tonal and broadband noise, management of denoising artifacts, and an editing interface for controlling reduction across the frequency spectrum.

Controls

Learn

When Learn is enabled, Spectral De-noise will capture a noise profile from your selection. After a noise profile is captured using Learn, it remains fixed for the duration of processing. Manually learned noise profiles are best suited to removing or reducing noise that is constant and continuous throughout the duration of the file.

How to Learn a noise profile in Spectral De-noise

More Information about Learning Noise Profiles

See the More Information section below to learn more about getting the best results when capturing a noise profile and Learning a noise profile from multiple selections in the RX 8 Audio Editor.

Adaptive Mode

When Adaptive Mode is enabled, the noise profile used for Spectral De-noise processing will change based on the incoming audio. Adaptive mode can work well with noise sources that are constantly changing, like recordings in outdoor environments, traffic noise, or ocean waves.

Spectral De-noise Adaptive mode Performance Note

Adaptive mode in Spectral De-noise uses a significant amount of memory and computational power. For a more efficient form of adaptive noise reduction, try the Adaptive mode in Voice De-noise, which is designed to be highly efficient and zero-latency.

Learning Time [s]

Determines the amount of lookahead time used by Adaptive mode when learning noise profiles that change over time.

Threshold (Noisy/Tonal)

Controls the amplitude separation of noise and useful signal levels.

Tip

If background noise changes in amplitude over time (like traffic noise or record surface noise), raise the Threshold to accommodate for the changes.

Reduction (Noisy/Tonal)

Controls the desired amount of noise suppression in decibels. Spectral De-noise can automatically separate noise into tonal parts (such as hum, buzz or interference) and random parts (such as hiss). You can specify the amount of suppression for these parts separately (e.g. in some situations it can be desirable to reduce only unpleasant buzz while leaving unobjectionable constant hiss).

Note

Strong suppression of noise can also degrade low-level signals, so it is recommended to apply only as much suppression as needed for reducing the noise to levels where it becomes less objectionable.

Quality

Affects the quality and computational complexity of the noise reduction. This selection directly affects CPU usage. RX’s Spectral De-noise module offers four algorithms that vary in processing time.

Artifact Control

Determines how much noise reduction will depend upon either spectral subtraction or wide band gating.

Noise Spectrum Display

The Noise Spectrum display shows useful information during both playback and when the noise reduction process is being applied.

Smoothing

When the Reduction Curve is enabled, this controls the amount of interpolation between your reduction curve points, allowing for sharper or more gradual slopes between edit curve points.

Reduction Curve

When enabled, allows for fine tuning of the reduction spectrum with up to 25 edit points. This enables you to customize the amount of noise reduction being applied across different frequency regions.

Interacting with the Reduction Curve Edit points

Reset

Returns the Noise Reduction Curve to its default setting of 0dB.

Advanced Settings

Algorithm Behavior (Advanced Settings)

Smoothing - Advanced

Controls the reduction of musical noise artifacts which can be a result of heavy denoising.

What is musical noise?

Musical noise is caused by random statistical variations of noise spectrum that cause random triggering of sub-band gates. These artifacts are sometimes described as “chirpy” or “watery” sounds left behind during the noise reduction process.

Algorithm

Selects the smoothing algorithm for the removal of random ripples (“musical noise” artifacts) that can occur in the spectrogram when processing your audio. The strength of smoothing is controlled by the Smoothing slider.

FFT Size (ms)

Selects the time and frequency resolution of the processing.

Re-learn your Noise profile if you change FFT size

If the FFT size is changed, it is recommended that you run the De-noise module’s Learn feature again because the old noise profile was taken at a different FFT size and therefore becomes inaccurate.

Multi-Res

Enables multi-resolution processing for the selected algorithm type. When you select the Multi-res checkbox, the signal is analyzed in real-time and the most appropriate FFT size is chosen for each segment of the signal. This is done to minimize the smearing of transients and at the same time achieve high frequency resolution where it is needed.

Note

The FFT size control does not have any effect in multi-resolution mode as the FFT resolution is selected automatically. The noise profile does not need to be re-learned when switching to multi-resolution mode.

Fast Fourier Transform (FFT)

A procedure for the calculation of a signal frequency spectrum. The greater the FFT size, the greater the frequency resolution, i.e., notes and tonal events will be clearer at larger sizes. However, when using FFT-based processing, the more audio you remove from your source, the more likely you are to create undesirable artifacts.

Noise Floor (Advanced Settings)

Dynamics (Advanced Settings)

More Information

Tips for getting the best results when learning noise profiles manually

Learning a Noise Profile From Multiple Selections

In the RX standalone application, it is possible to create a spectral profile from multiple isolated selections. This is useful when you have a file where it’s impossible to find enough isolated noise to build the profile.

For example, if you are trying to restore a file where someone is speaking over noise, you can select noise in frequencies where none of the voice is present at a given time. If you select enough of this noise with the Lasso or Brush selection tools, you can create an accurate noise profile that will give you good results with Spectral De-noise. You can create more than one selection at a time by holding Shift while making a selection.

Select noise anywhere you can to build a better noise profile.

This feature is not available in the Spectral De-noise plug-in because it requires using RX’s spectral selection tools as well as accurate calculation of the time and frequency of the selected areas. If you are unable to create a full noise profile with multiple selections, RX can try to build a reasonable noise profile out of your existing profile. If you have an incomplete noise profile, RX will ask you if you want it to complete the profile.

For example, if you can only capture a low frequency rumble below 100 Hz, some broadband noise between 200 Hz and 5000 Hz, and all the noise above 8000 Hz, RX can fill in the gaps for you. Building a profile from multiple selections gives you some flexibility, and RX will guess any noise you missed.

RX 8.5.0

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