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

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)

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’

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.)

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

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

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.)

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

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

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.

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

SOUNDS RECORDING AND REPRODUCTION Violin Wave Shape - 10 Harmonics

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

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

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

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

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

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

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

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!