Electronics Projects: Spectrogram

Implementation of Speech Spectrogram using Matlab GUI

A spectrogram is a visual representation of the spectrum of frequencies in a sound. Spectrograms are sometimes called spectral waterfalls, voiceprints, or voicegrams. Spectrograms can be used to identify spoken words phonetically, and to analyze the various calls of animals. They are used extensively in the development of the fields of music, sonar, radar, and speech processing, seismology, etc. Spectrograms are usually created in one of two ways: approximated as a filter bank that results from a series of band pass filters (this was the only way before the advent of modern digital signal processing), or calculated from the time signal using the short-time Fourier transform (STFT). These two methods actually form two different Time-Frequency Distributions, but are equivalent under some conditions.

Creating a spectrogram using the STFT is usually a digital process. Digitally sampled data, in the time domain, is broken up into chunks, which usually overlap, and Fourier transformed to calculate the magnitude of the frequency spectrum for each chunk. Each chunk then corresponds to a vertical line in the image; a measurement of magnitude versus frequency for a specific moment in time. The spectrums or time plots are then "laid side by side" to form the image or a three-dimensional surface.

             This project provides the implementation of spectrogram with Matlab GUI to make this project user friendly.

Applications:

• Early analog spectrograms were applied to a wide range of areas including the study of bird calls, with current research continuing using modern digital equipment and applied to all animal sounds. Contemporary use of the digital spectrogram is especially useful for studying frequency modulation (FM) in animal calls. Specifically, the distinguishing characteristics of FM chirps, broadband clicks, and social harmonizing are most easily visualized with the spectrogram.
• Spectrograms are useful in assisting in overcoming speech defects and in speech training for the portion of the population that is profoundly deaf
• The studies of phonetics and speech synthesis are often facilitated through the use of spectrograms.
• By reversing the process of producing a spectrogram, it is possible to create a signal whose spectrogram is an arbitrary image. This technique can be used to hide a picture in a piece of audio and has been employed by several electronic music artists.
•  Some modern music is created using spectrograms as an intermediate medium; changing the intensity of different frequencies over time, or even creating new ones, by drawing them and then inverse transforming.
• Spectrograms can be used to analyze the results of passing a test signal through a signal processor such as a filter in order to check its performance.
• High definition spectrograms are used in the development of RF and microwave systems.
• Spectrograms are now used to display S-parameters measured with vector network analyzers