1. Harmonics and Overtones Waveforms / Wave Interaction Phase Concepts / Comb Filtering Beat Frequencies / Noise AUD202 Audio and Acoustics Theory

2. Last Week > Frequency and Dynamic Ranges of Hearing Frequency / Wavelength / Period / Speed

3. Upcoming Assessments Week 8 - NIHL Report Week 11 - Sound Observations Report Week 13 - Exam

4. Units of Measurement = velocity of sound (in metres per second) = wavelength (in metres) = frequency in Hertz (Hertz is cycles per second) = period of one cycle (in seconds)

5. HARMONICS & OVERTONES

6. Harmonics are integer multiples of the fundamental frequency.

7. Harmonics For example, if the fundamental frequency is 200Hz, the harmonics would be: 200Hz 400Hz 600Hz 800Hz 1000Hz Fundamental frequency 2 nd harmonic 3 rd harmonic 4 th harmonic 5 th harmonic

8. An overtone is any frequency higher than the fundamental frequency of a sound..

9. SIMPLE WAVEFORMS

10. Fundamental frequency only, no harmonics Sine Wave

12. Odd and even harmonics at inverse amplitudes Sawtooth Wave

13. Odd harmonics at inverse amplitudes Square Wave

14. Odd harmonics at inverse squared amplitudes Triangle Wave

15. Making a sawtooth from a sine wave A sawtooth wave's sound is harsh and clear and its spectrum contains both even and odd harmonics of the fundamental frequency

16. Simple Harmonic Motion Constant frequency without regard to amplitude

17. Simple Harmonic Motion

18. PHASE

19. Phase Concepts The word ‘Phase’ is used to describe a specific location in a cycle of a periodic (repeating) wave “In phase”, “out of phase” and “completely out of phase” are terms used to describe relative positions of a wave cycle

20. Phase Concepts

21. Phase Angles

22. Wave Interaction Two sine waves with the same amplitude and frequency can add either destructively or constructively depending on their relative phase

23. Two sine waves travelling in opposite directions can create a standing wave

24. Beat Frequencies

25. When two sound waves of different (but close) frequencies are played together, the alternating constructive and destructive interference causes an oscillation of the resulting waveform frequency 1 – frequency 2 = Beat frequency 502 Hz - 500 Hz = 2 beats per second

26. COMB FILTERING

27. Comb filtering is caused by a wave combining with a delayed version of itself

28. Comb Filtering A wave delayed by 180 degrees (half a wavelength) results in the fundamental frequency of cancellation. Frequencies delayed by 1.5x, 2.5x, 3.5x the wavelength will cancel, while whole number multiples (1, 2, 3 etc) will reinforce.

29. Comb Filtering A wave delayed by half a wavelength results in the fundamental frequency of cancellation.

30. Single signal, no comb filter issues

31. 1ms delayed version of the signal added

33. Comb Filtering Common causes of comb filtering: 1.Two microphones at different distances from the same source. 2.Reflective nearby surface causing a reflected sound to arrive at the microphone slightly after the direct sound. 3.Two identical sounds in a DAW with a 1 to 10ms delay

34. WHITE NOISE & PINK NOISE

35. Noise White noise: Equal energy per frequency Pink noise: Equal energy per octave Pink noise is simply White noise with a ‘pinking filter’ added (-3dB/octave roll off)

37. Speed Writing Exercise List anything that might cause NIHL List occupations where NIHL might be a problem List ways to avoid NIHL

39. Next Week > Sound Envelopes Instrument Acoustics