Let us start with a single tone sound:
1. Open the file named tone800Hz.wav from C:\Program Files\Stethographics\STG1\STG Examples directory.
2. Listen to the sound.
3. Switch to Spectrogram Display. The spectrogram shows a single line at 800Hz. This tells us that all the energy of the signal is concentrated at 800Hz.
4. Sounds you normally hear are composed of a number of tones played simultaneously. Record the sound of you, speaking into the electronic stethoscope or a microphone. Switch to the Spectrogram Display. The spectrogram shows a number of high energy bands. These bands correspond to a number of tones of different pitch and amplitude that combined together make the sound of your voice. Sound spectrum is just a decomposition of the sound into a number of tones, the process that allows us to find out the pitch and the amplitude of these tones.
II. Sound pitch
Pitch or frequency is expressed in Hertz (Hz), named after German physicist Heinrich Rudolf Hertz (1857 to 1894), who demonstrated the nature of electromagnetic waves propagation. Our ears can hear tones from 15Hz to 20,000Hz. What we usually call low pitch tone corresponds to approximately 15Hz to 300Hz. To play a low frequency tone:
1. Open the file named tone150Hz.wav from C:\Program Files\Stethographics\STG1\STG Examples directory
2. Listen to the sound
Tones higher than 300Hz are usually referred to as high pitch tones. To play a high frequency tone:
1. Open a file named tone800Hz.wav from C:\Program Files\Stethographics\STG1\STG Examples directory
2. Listen to the sound
sound sounds higher?
III. Crackles and Wheezes visualization
STG can visualize sounds in time and frequency domains.
Crackles are intermittent explosive sounds that have been described as being similar to the crackling sound heard as wood burns. Crackles appear in the time domain as intermittent spike-like deflections. They can be seen in the unexpanded display but are usually seen more readily in the expanded mode. Crackles are divided into two types, fine and coarse by their acoustic properties. On auscultation fine crackles are in general higher pitched, less intense and of shorter duration than coarse crackles.
Wheezes are described as relatively continuous sounds as compared to crackles. They usually last for more than 200 milliseconds and have a musical quality. On time expanded waveform analysis they can be seen to have a sinusoidal pattern.
It is generally accepted that time domain is convenient for visualization of the short-lived sounds like crackles and short wheezes, while the frequency domain is is more useful for observing sounds of long duration, like wheezes.
To visualize wheezes and rhonchi:
IV. Summary of Crackles and Wheezes Recorded from Multiple Sites
The software contains the algorithm that identifies and counts crackles and wheezes. The count is indicated at the bottom of the STG screen. Fine and Coarse counts are presented as crackles per second; the wheeze rate is the percentage of the time in which wheezes were detected. In default crackles and wheezes are counted over 10 seconds and the average count is indicated. When any region of waveform display is highlighted, the count is recalculated to represent the average crackle and wheeze count over the highlighted region.
Summary display assists in visualizing crackle and wheeze counts from
multiple sites. Since you are using 1 channel STG, the data collection
process is sequential, from one site at a time. We, at Stethographics,
have developed a 16 channel STG system that collects data from 16 chest
sites simultaneously. Lung sounds recording from multiple sites not only
streamlines the auscultation but also greatly improves the diagnostic
process. For example 16 channel STG automatically calculates the location
of the origin of crackles and wheezes inside the chest. You can see examples
of crackles and wheezes localization at Physiology
section of this site.