Learn Music and Audio Production | iZotope Tips and Tutorials

Understanding the Spectrogram/Waveform Display

January 20, 2005

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RX 8

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What is a Spectrogram?

A spectrogram is a very detailed view of your audio, representing time, frequency, and amplitude all on one graph. The spectrogram can let you see at a glance where there is broadband, electrical, and intermittent noise, and allows you to easily isolate audio problems by sight.

Spectrogram versus Waveform

In audio software, we’re accustomed to seeing a waveform that displays changes in a signal’s amplitude over time. But the spectrogram displays the audio signals by time and by frequency—showing the frequency components that make up the signal. Amplitude is then represented on a third dimension with variable brightness or color.

Let's take a look at an audio file using a traditional waveform view and using a spectrogram.

Here is a sine wave moving up in pitch from 60 to 12,000 Hz as seen in a traditional waveform.

You’ll notice that the waveform shows audio amplitude across time, but we can not really see what’s happening at individual frequencies. We can see that the sine wave is the same level for the entire duration of the file, but we can’t tell much about how the pitch or frequency changes over time.

Here is the same audio file using a spectrogram.

In the spectrogram view, the vertical axis displays frequency in Hertz, the horizontal axis represents time (just like the waveform display), and amplitude is represented by brightness.

The black background is silence, while the bright orange curve is the sine wave moving up in pitch. This allows us to view a range of frequencies (lowest at the bottom of the display, highest at the top) and how loud events are at different frequencies. Loud events will appear bright and quiet events will appear dark.

Now let’s look at a more complex audio example: the human voice.

Here’s a short, spoken phrase as seen through a waveform display. What we see here is the amplitude of the spoken words over time.

If we switch to the spectrogram view, we’ll see many things we can’t see in the waveform view.

This is why having a detailed spectrogram display is so important in audio editing. It helps to clearly display the problems that you might want to fix.

The Spectrogram/Waveform Display in RX

RX features an advanced spectrogram display that is capable of showing greater time and frequency resolution than other spectrograms, allowing you to see an unprecedented level of detail when working with audio.

An overview of the entire audio file's waveform will be displayed above the main Spectrogram/Waveform display in a Waveform Overview. The Waveform Overview will always display the entire audio file and will also display any selections made in the main display.

You can also view the traditional waveform, or a blend of both, by adjusting the Waveform/Spectrogram Opacity slider to the left just below the spectrogram.

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