Stridor Respiratory Sounds (Educational wav-file)

Sound at the chest surface or at the neck was recorded with contact accelerometers (EMT25C, Siemens). Recordings at the mouth were made with an electret microphone (ECM140, Sony).
Air flow was registered with a screen pneumotachograph (model 3350, Spirometrics). Inductance plethysmography (Respitrace) was used in young children to provide information about the respiratory pattern.
The sound signal was high-pass filtered at 7.5 Hz to remove DC offset (1st order Butterworth filter) and low-pass filtered at 2.5 kHz to avoid aliasing (8th order Butterworth filter). The original sampling rate was 10 kHz (some files were upsampled from 5 kHz).
Analog-to-digital conversion was performed with 16-bit quantization (AT-MIO-16x, National Instruments), using a notebook PC and R.A.L.E.® software. Some files were originally acquired with 12-bit quantization (model 2801, DataTranslation) and have been adjusted for 16-bit presentation.
Signal processing involved fast Fourier transformation analysis (Hanning data window, 1024 data points, 75% overlap).