Complex Auditory Stimuli

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Presentation transcript:

Complex Auditory Stimuli Complex periodic waves Complex aperiodic waves

Complex Periodic Waves Addition of sine waves See next slide for examples Always repeat themselves over time … and therefore have a period. Always have a fundamental frequency Fundamental is the largest common denominator of a group of component frequencies Always have harmonic frequencies Harmonics are are whole number multiples of the fundamental e.g., 1f, 2f, 3f, etc.

Periodic Complex Waves

Periodic Complex Waves

Periodic Complex Waves

How are complex periodic waves displayed? Waveform Amplitude Spectrum (line spectrum)

How are complex periodic waves displayed? Several examples of a line spectrum. The lower figure represents the vowel / i /.

Fundamental Frequency See earlier slide. Largest common denominator of a group of component frequencies. E.g., If the the component frequencies are 500, 550, 1000, 1050, the largest number that can be evenly divided would be 50. Therefore, 50 Hz would be the fundamental. It would also have the same pitch as a 50 Hz tone.

Harmonics Harmonics are whole number multiples of the fundamental (fo). The fundamental is always the first harmonic (1f). May be determined by dividing the fo into the component frequency. In the previous example the component frequencies would equal the following harmonics. 500 Hz = 10xf (i.e., 10th Harmonic) 550 Hz = 11xf 1000 Hz = 20xf 1050 Hz = 21xf

Harmonics Relationship between harmonics and overtones. Overtones are a musical term and are related to harmonics.

Complex Aperiodic Waves Frequencies are random Do not repeat over time Do not have a fundamental frequency Do not have harmonics

How are complex aperiodic waves displayed? Waveform Amplitude spectrum (continuous spectrum)

How are complex aperiodic waves displayed?

How is Sound Analyzed? Spectrogram (aka sonogram) Sound level meter Oscilloscope and frequency counter Fourier and real time analyses

Spectrogram

Sound Level Meter

Sound Level Meter Sound Pressure Level (linear) dBA, dBB, dBC (weighted scales)

Sound Level Meter dBA, dBB, dBC (weighted scales) Used primarily for industrial, community, and aviation applications. dBA scale has greatest amount of attenuation in low frequencies. dBB scale somewhat inbetween dBA and dBC. dBC scale has least amount of attenuation in high frequencies.

Other Methods of Analysis Oscilloscope (displays waveform)

Other Methods of Analysis Frequency Counter

Other Methods of Analysis Fourier Analysis A method of mathematically changing a waveform to an amplitude spectrum Real Time Analysis or Fast Fourier Transform (FFT). Fourier analysis in real time

Summary