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Amplitude

Amplitude. Measure of the magnitude of the oscillation. How great the increase and decrease in air pressure produced by a vibration. Perceived as volume. Decibel. The most common scale for measuring amplitude. A relative scale.

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Amplitude

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  1. Amplitude Measure of the magnitude of the oscillation. How great the increase and decrease in air pressure produced by a vibration. Perceived as volume.

  2. Decibel • The most common scale for measuring amplitude. • A relative scale. • The difference in amplitude between two sounds is represented as a decibel.

  3. Decibel scales • SPL (Sound pressure level). • Begins at 0dB (minimum point at which the human ear can just perceive a 1000 Hz tone) • That is the reference point. • Extends to 130 dB - roughly the level that causes pain to the ear. • Chart on P. 86

  4. Decibel scales • VU (volume unit). • Unit of measuring amplitude found on analog equipment (VU meters). • Reference point of 0 dB is the MAXIMUM amplitude recommended for recording on that equipment. • Anything above 0 dB will experience distortion. • Readings below this are recorded as negative values.

  5. Decibel scales • FS (full scale). • Used on digital recording equipment. • 0 dBFS is the MAXIMUM level at which a sound can be recorded. • Beyond 0 dB FS, clipping occurs (the digital version of distortion). • Middle line is infinity - smaller values, including those that are imperceptible.

  6. Envelope • Measurement of the “life cycle” of a tone. • Attack • Decay • Sustain • Release

  7. Envelope • Attack - the initial sound of a tone

  8. Envelope • Decay - the decrease in amplitude after the attack of a tone

  9. Envelope • Sustain - the amplitude once it has “settled in”

  10. Envelope • Release - the time it takes for the instrument to stop vibrating and come to a complete state of rest.

  11. Envelope • Each instrument type has a specific shape of its envelope • Largely based on how it produces sound (plucking, air, striking, etc.)

  12. File sizes • 44.1 kHz sampling rate at 16-bit • Roughly 10 MB per minute per channel • A 5 minute song recorded in stereo will use 100 MB.

  13. File sizes • Bit - “BInary digIT” • The resolution of the sampling (a number is used to represent each sample) • Bit depth is typically 8-, 12-, 16-, or 24-bit numbers. • The larger the bit rate, the more physical storage space it will take up. • Compare to megapixels for cameras?

  14. Compression • Lossy - data is lost • Lossless - restores all data to original form.

  15. Compression • MP3 format uses 2 lossy and 1 lossless techniques. • Threshold of hearing (lossy). Eliminates sounds below the human threshold of hearing • Masking (lossy). Loud sounds cover up softer sounds. Softer sounds that are masked are eliminated. • Redundancy of information (lossless). Repeated patterns summarized algorithmically when recording, and expanded during decoding.

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