PH 105

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# PH 105 - PowerPoint PPT Presentation

PH 105. Dr. Cecilia Vogel Lecture 13. OUTLINE. Timbre and graphs: Time graph Spectrum graph Spectrogram Envelope scales units interval factors. Fourier Analysis. Fourier Synthesis meant from the spectrum, build the Fourier Analysis means from the waveform, find the

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Presentation Transcript
PH 105

Dr. Cecilia Vogel

Lecture 13

OUTLINE

• Timbre and graphs:
• Time graph
• Spectrum graph
• Spectrogram
• Envelope
• scales
• units
• interval factors
Fourier Analysis
• Fourier Synthesis meant from the spectrum, build the
• Fourier Analysis means
• from the waveform, find the
• Let’s let the computer do it.
• This yields a spectrum graph
• or ____ graph
• Amplitude vs
Pitch and Timbre —Graphs
• Dominant influences on pitch and timbre:

*f1 might be lowest freq, but might not

*Often overtones are nf1.

Envelope
• Envelope is the time variation of the sound
• Often divided into:
• attack = initial building up of sound
• decay = decrease to sustained level
• or to zero, if the sound is not sustained
• sustain = sound held fairly steady
• release = final decrease of sound to zero

A

D

S

R

• Attack, decay, and release
• Are usually described by the time they last
• Sustain
• is usually described by the level (amplitude)
• But all four may have their own
• frequency, spectrum, amplitude, and duration
Spectrograms
• time graphs
• show time variation (x-axis is time)
• spectrum graphs
• show frequencies in spectrum (x-axis is frequency)
• Spectrograms
• show both
• x-axis is time
• y-axis is frequency
• Amplitude is shown by heaviness of graphing
Bird Song Spectrograms
• Top one (a)
• three trills
• many freq’s — noise-like
• Bottom one (b)
• first a low tone with many harmonics
• rises and falls slightly
• then higher, purer tone
• falls slightly
• finally lower, more noise-like tone
Octave
• If two pitches
• the frequency of one is
• fundamental similarity in
• Octaves are further divided
• into cents, semitones, whole tones
Cents
• One cent interval has a ratio of 1.0006
• 1 cent above 440Hz is
• Can you tell the difference between 440 Hz and 440.25 Hz?
• a jnd is a ratio of 1.005
• 10 cent above 440Hz is
• Can you tell the difference between 440 Hz and 442.55 Hz? (10 cents)
Cents Calculation
• Interval, I, in cents is related to the
• Example, an octave has a ratio of
Semitone
• An octave is often
• each semitone is a factor of
• multiply 440 Hz (an A) by
• you’ll get about 880 Hz
• Keys on a piano are separated by
• 12 semitones in order is a
Musical Staff
• Musical notes are
• the x-axis is
• the y-axis is
• Fig 8.9
• Only the notes in spaces are written in.
• Notes on lines are letters between.
• Short lines indicate where sharp/flat would be , graphically.
Major Diatonic Scale
• Western music uses a ____________ instead.
• A major diatonic scale has
• (the 8th would be an
• The intervals are not all semitones
• some are
• whole tone is about a factor of (1.06)2 = 1.12
• The intervals in major diatonic scale are
• You’ve played a major diatonic scale.
Example
• Key of C (major diatonic scale)
• play
• CDEFGAB
• C to D is a
• C#/Db is between
• similarly with
• E to F is a
Scale on Piano
• one octave on keyboard
• ignore the gray for now

Summary