EECS150 Digital Design Lecture 13 Final Project Description

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EECS150 - Digital DesignLecture 13 - Final
Project Description

• March 7, 2002
• John Wawrzynek

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Project

• Everyone will design, debug, and demonstrate a
  Music Synthesizer
• Operation based on principle of waveform
  synthesis or sampling.
• Sounds from recordings of real musical
  instruments are stored in memory then
  pitch-shifted and played back in response to note
  commands.
• 1 or 2 partners/group

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Digital Waveforms

• In digital systems waveforms are represented as a
  series of numbers, rather than a voltage or
  current, as in analog systems.
• Example sound waveform
• Sound can be produced by sending series of
  numbers to Digital to Analog converter, then to
  Amplifier, then to speaker.
• In principle any sound can be produced.

Sampling rate 31.25KHz 16-bits per sample
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Interfaces

• MIDI Musical Instrument Digital Interface.
• Commands are sent from a keyboard (or computer)
  to control the synthesizer.
• Waveforms are stored in the ROM (read only
  memory).
• Monophonic one voice at a time.

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Theory of Sound and Music

• Air vibrating in the frequency range of 20Hz to
  20KHz is perceived as sound.
• The three important characteristics of perceived
  sound are
• loudness (relates to amplitude)
• pitch (relates to frequency)
• timbre (relates to shape)
• Human hearing is approximately logarithmic in
  perceiving loudness and pitch
• we perceive the loudness as being prop to the log
  of the sound wave amplitude

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Timbre

• tone quality or color
• Different instruments have different timbres.
• We perceive timbre based on how a note begins,
  repeats, and ends.
• For many instruments a simple model can be used
  to represent the shape of the waveform.
• Attack, sustain, release (decay)
• Works best for driven instruments woodwinds,
  brass, bowed strings.
• Pluck and struck instruments dont have the
  sustain

picture
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Pitch

• Middle C has frequency of 261.63Hz.
• MIDI encoding of 60
• High C (an octave above middle C) has frequency
  523.25Hz
• MIDI encoding of 72
• Other tones can be produced by multiplying and
  dividing the frequency by factors of 12th root of
  2.

• Pitch
• 12 semi-tones form the chromatic scale of the
  western scale.
• To move from one up to the next
• freqnext freq 12th root of 2.
• After 12 such multiplications we will have
  doubled the freq and reached the octave.
• Most people can detect pitch differences as small
  as a few hundreds of a semi-tone (or a few times
  the 1200th root of 2)!

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Playing Notes

• ROM used to store notes has limited capacity.
• For notes with sustain portion, would like to
  vary note duration

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Pitch Shifting
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Pitch Shifting
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Linear Interpolation
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ROM (EEPROM) Layout

• One stored note per instrument is never enough.
• Timbre varies from note to note over the range of
  the instrument.
• ROM holds directory with one entry per MIDI note
  number.
• Entry holds pointer to note template and step
  size.
• Note step sizes are precomputed (synthesizer does
  not need to do 12th root of 2 calculation.
• One instrument per ROM (might change this later).

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Directory Entry Layout

• 20-bit template pointer

• 12 bits of step size

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Template Layout
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Instrument Template Files

• We will provide you with template files and a
  program for converting these to EPROM format.
• We also have programs for taking instrument
  samples from standard file formats and converting
  them to our template format. You are encouraged
  to generate your own template files and EPROMs.
• We might extend the format (and project) to allow
  for more than one instrument per EPROM.
• Switch among the instruments either through dip
  switches or MIDI commands.

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High-level Block Diagram
FSM and datapath for each block.
This is only a suggestion. Your organization is
up to you.
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Checkpoints

• 3/11 UART Design and Test
• 3/18 ROM Interfacing
• 3/25 Recess
• 4/1 MIDI Interface
• 4/1 Audio Stage
• 4/8 Monotone Notes
• 4/15 Notes of Arbitrary Frequency
• 4/22 Velocity Sensitivity
• 4/29 Spare
• 5/6 Final Checkoff

• Your are strongly suggested to work ahead.
• These are only minimum requirements.
• Completion of checkpoints are part of your
  project grade.
• Project spec document online today.
• All checkpoint write-ups available in next couple
  days (in draft form).

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Extra Credit

• Early Final Checkoff.
• 1 week or more
• Low CLB Count.
• low quantified later
• Interpolation
• add linear interpolation for sample lookup
• Polyphony.
• The ability to play multiple keys at once
• Velocity Sensitive Template Lookup.
• Index templates not only on key number but also
  velocity.

• Extra credit only considered for fully functional
  designs.
• Point assignment announced later. Usually in the
  15 range.

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Connections
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Note On
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Note off
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Keyboard Mapping
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Running Status

• The MIDI standard convention allows a transmitter
  to compress the data stream by dropping status
  bytes.
• A command without a status byte implicitly uses
  whatever status byte was most recently sent.
• Therefore a keyboard can send a sequence of
  note-on and note-off commands only the first of
  which having a status byte.
• Your synthesizer must conform to the running
  status convention.