Activity 05 - Spectrograms

Spectrograms

A spectrogram is a graph of a sound wave's component frequencies over time. Component frequencies are the range of frequencies present in the sound.

A spectrogram shows time on the x-axis and frequency on the y-axis. That means the bottom of the spectrogram is the lowest frequency, and the top is the highest frequency. Moving left to right on the spectrogram represents moving forward in time.

A spectrogram also shows a third dimension: amplitude (loudness). Differences in amplitude are shown as differences in color or darkness on the spectrogram. The darker lines are frequencies with higher amplitude, while the lighter areas are frequencies with lower amplitude.

Obtaining Spectrograms using Audacity

Audacity is an easy-to-use, multi-track audio editor and recorder for Windows, macOS, GNU/Linux and other operating systems.

Audacity is free, open-source software.

This was done using the sarigamapa.wav file

Waveform of the sarigamapa.wav file

Obtained spectrogram of the wav file using audacity

Window type: Hann

Window size: 2048

Frequency analysis

Window size of a spectrogram

The window size of a spectrogram refers to the number of audio samples that are analyzed at a time in order to compute the frequency content of the signal. The window size is usually specified as a number of samples, and it is one of the parameters that can be adjusted when creating a spectrogram.

A small window size will result in a high frequency resolution, but a low temporal resolution. This means that the spectrogram will show a lot of detail in the frequency domain, but it will not be able to accurately represent changes in the audio signal over time.

On the other hand, a large window size will result in a high temporal resolution, but a low frequency resolution. This means that the spectrogram will be able to accurately represent changes in the audio signal over time, but it will not show as much detail in the frequency domain.

The most common window sizes used in spectrograms are powers of two, such as 256, 512, 1024, etc. The window size is usually set according to the desired trade-off between frequency and temporal resolution, as well as the characteristics of the audio signal being analyzed.

Additionally, it is worth noting that the window type can also affect the spectrogram, different window functions such as Hamming, Hanning, Blackman, etc. have different properties that can be used to make the spectrogram more appropriate for the signal being analyzed.

In Audacity, you can change adjustments of the spectrogram such as the window size, Window overlap and Window type.

Changing the window type while keeping the window size at 2048