Understanding the Spectrogram/Waveform display - Help Documentation

May 2024 · 8 minute read

Overview

The RX Audio Editor features a rich visual environment for editing and repairing audio. The central focus of the interface is the Spectrogram/Waveform display. It combines an advanced Spectrogram with a waveform transparency overlay to provide frequency and amplitude information in one highly configurable window.

Using the spectrogram to identify audio problems

ANATOMY OF THE SPECTROGRAM DISPLAY

The spectrogram allows you to visualize both frequency and amplitude information of an audio recording in one display.

FREQUENCY

The Spectrogram shows frequency information across the vertical axis. Lowest frequency content is displayed at the bottom, highest frequency content is displayed at the top.

Spectrogram Sine Sweep
This image shows the spectrogram of a sine sweep over pink noise. The sine sweep starts at 20 Hz (bottom of the display) and sweeps to 20 kHz (top of the display) over 4 minutes.

AMPLITUDE & COLOR

The amplitude of frequency content is indicated by variations in color in the Spectrogram. The color map ruler (to the right of the frequency ruler) shows the color being used to represent a given amplitude value.

spectrogram color map
In this example, Louder events (speech) are indicated by brighter colors (yellow/bright orange) and quieter events (breaks in speech and noise floor) are indicated by darker colors (dark orange, blue, black)

Spectrogram Settings

The RX Spectrogram is highly configurable, you can adjust the default configuration, load a preset or save your own preset in the Spectrogram Settings window.

The Spectrogram Settings window can be opened:

Spectrogram Settings

TYPEDESCRIPTIONEXAMPLE
REGULAR STFTMost common spectrogram type (can be found in other editors) It has a fixed uniform time-frequency resolution. This is the simplest and fastest drawing mode in RX.RegularSTFT
AUTO-ADJUSTABLE STFTAutomatically adjusts FFT size (i.e. time and frequency resolution of a Spectrogram) according to the zoom level. For example, if you zoom in horizontally (time) you’ll see that percussive sounds and transients will be more clearly defined. When you zoom in vertically (frequency), you’ll see individual musical notes and frequency events will appear more clearly defined.Auto Adjustable STFT
MULTI-RESOLUTIONCalculates the Spectrogram with better frequency resolution at low frequencies and better time resolution at high frequencies. This mimics psychoacoustic properties of our perception, allowing the Spectrogram display to show you the most important information clearly.Multi resolution
ADAPTIVELY SPARSEAutomatically varies the time and frequency resolution of the Spectrogram to achieve the best Spectrogram sharpness in every area of the time-frequency plane. This often lets you see the most details for a thorough analysis, but it’s the slowest mode to calculate.Adaptively sparse

What does FFT mean?

Fast Fourier Transform: 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.

Rulers

On the right side of the Spectrogram/Waveform display are the Amplitude ruler for the Waveform, Frequency ruler for the Spectrogram, and Color Map ruler for the Spectrogram.

Amplitude Rulers

You can right-click on the spectral Amplitude ruler to reveal a selection of amplitude scales:

Color Map Ruler

This ruler shows what color represents what amplitude in the Spectrogram. The range of this display is the dynamic range of the RX Spectrogram. You can click and drag the map to change the range and use the scroll wheel to make the range larger or smaller. This is useful for seeing very quiet noises without using gain to change the level of your audio.

Frequency Rulers

Right-clicking on the frequency ruler will display the frequency scale options:

Waveform Displays

Waveform Transparency Balance Slider

Transparency Slider

The Spectrogram Display features a transparency slider that lets you superimpose a Waveform display over the Spectrogram, allowing you to see both frequency and overall amplitude at the same time. This can be invaluable for quickly identifying clipping, clicks and pops, and other events.

Below are examples of the same clip shown with different transparency balance values:
spectrogramwave & spectrogram
mostly waveformwave only

Waveform Overview

Audio Waveform Above Main Display

An overview of the entire audio file’s Waveform is displayed above the main Spectrogram/Waveform display in order to provide a handy reference point when zooming and making audio selections in RX.

The Waveform overview will always display the entire audio file, and will also display any selections made in the main display.

When zooming in on your audio, the currently visible audio region will also be highlighted in the Waveform overview. Click and drag on the highlighted region in order to scroll your main audio display left or right, and click and drag on the edges of the highlighted region in order to make the zoom tighter or wider. To zoom out fully, simply double click on the highlighted visible region.

Note

With your mouse hovering over the Waveform overview, you can also use the mouse wheel to scale the amplitude of the Waveform display to provide a clearer overview. This will not affect the amplitude scaling in the main Spectrogram/Waveform display.

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