1. SOUNDS RECORDING AND REPRODUCTION The Volume of the Wave n The Amplitude is a measure of volume n The wave pink is softer than the blue wave. n It represents both air pressure variations, and the displacements of the source, the air particles, and our ear drums, enabling us to hear

2. SOUNDS RECORDING AND REPRODUCTION The Pitch of a sound wave n The pitch is determined by the frequency, or how often (frequently) a full wave reaches our ears n The higher the frequency, the higher the pitch n The pink wave below has a higher pitch than the blue wave (by an octave - discussed later)

3. SOUNDS RECORDING AND REPRODUCTION The Guitar - Pitch Control Factors affecting the pitch included:- 1. The Length - placing fingers on the fretboard shortens the string, and increases the pitch 2. The Mass / Unit Length (or thickness) - low bass strings are thicker 3. The Tension - tuning & using ‘vibrato’ and ‘bends’

4. SOUNDS RECORDING AND REPRODUCTION Standing Waves - Strings Key Results Harmonics form a series with frequencies given by f, 2f, 3f,4f... i.e. All Harmonics are present. (f = First Harmonic freq.)

5. SOUNDS RECORDING AND REPRODUCTION The Tone or Timbre n Most instruments (and voices) have a combination of possible vibrations occurring at the one time. n The next few slides attempt to show how this results in a characteristic wave shape for each instrument, which determines its tone (timbre) n This helps us distinguish between different instruments playing the same pitch and volume

6. SOUNDS RECORDING AND REPRODUCTION The Fundamental Frequency n This is the first harmonic. n It determines the pitch of the note we hear n It is the same for all different instruments playing the same pitch

7. SOUNDS RECORDING AND REPRODUCTION Standing Waves - Open Pipe Key Results Harrmonics form a series with frequencies given by f, 2f, 3f,4f... i.e. All Harmonics are present. (f = First Harmonic freq.)

8. SOUNDS RECORDING AND REPRODUCTION The Flute - First 2 Harmonics n The fundamental (first harmonic) is shown in blue n The second harmonic is shown in pink n The black line shows the sum using superposition -2 -1.5 -0.5 0 0.5 1 1.5 2

9. SOUNDS RECORDING AND REPRODUCTION Harmonic Spectrum - Flute n As the flute is a pipe which is open at both ends, all possible harmonics are present, but with different amounts of each. The Harmonic Spectrum shows how much of each is present. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 12345678

10. SOUNDS RECORDING AND REPRODUCTION The Flute - first 8 harmonics n The graph shows the resulting wave from adding the first 8 Harmonics in the correct amounts, using the superposition principle.

11. SOUNDS RECORDING AND REPRODUCTION Harmonic Spectrum - Violin n The harmonic spectrum of the violin displays a relatively high amount of the upper harmonics, resulting in a “bright” tone

12. SOUNDS RECORDING AND REPRODUCTION Violin Wave Shape - 10 Harmonics

13. SOUNDS RECORDING AND REPRODUCTION Closed Pipes -The Clarinet n The clarinet is a good example of an instrument which is effectively a pipe closed at one end n The result is a wave made from only the odd numbered harmonics n The Harmonic series is then: f, 3f, 5f, 7f, etc

14. SOUNDS RECORDING AND REPRODUCTION Clarinet Wave - 1st 4 odd harmonics n Note how the absence of even harmonics changes the overall form to be more like a square wave

15. SOUNDS RECORDING AND REPRODUCTION dB and Equipment Ratings n To provide a noticeable 3 dB increase in Volume of a Stereo, the power of the system must be doubled if it was running before at max. output. n The frequency response of equipment is usually quoted as a frequency range which can be reproduced +/- 3dB. (e.g. Microphones, Speakers, etc.) Frequency Output in dB Frequency Response eg 25 Hz - 18 kHz 3dB

16. SOUNDS RECORDING AND REPRODUCTION Graphic Equalisers and dB n A Graphic Equaliser changes the shape of the Frequency response curve by dividing it into sections n Each slider adds or subtracts to the dB level of each frequency band

17. SOUNDS RECORDING AND REPRODUCTION The Dynamic Microphone n Dynamic mics have a coil attached to a diaphragm suspended in the magnetic field of a magnet n Pressure changes cause the diaphragm to vibrate, changing the amount of magnetic flux threading the coil – inducing a current in the coil to produce a signal

18. SOUNDS RECORDING AND REPRODUCTION The Condensor Microphone n Condensor mics have two charged plates, the front one of which is very thin, and usually covered in a very fine gold layer n Pressure changes cause the front plate vibrate, changing the distance between the plates. This changes the capacitance of the system n A Voltage is supplied to plates, and thus the amount of charge on the plates varies, causing a current to produce the signal

19. SOUNDS RECORDING AND REPRODUCTION Microphone Responses n Condensor mics tend to have a much smoother frequency response, and are often used for recording n Dynamics have peaks designed to gain clarity with stage vocals

20. SOUNDS RECORDING AND REPRODUCTION Speaker Design n Resonance of a speaker has a critical effect on its frequency response n Designs employing closed cabinets with ports to minimise resonance work well n The sound of a system results from a combination of physics factors!