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Electronic Guitar Tuner

Electronic Guitar Tuner. K. Wettstein A. Wunderlich Senior Design Project Team 45 May 3, 1999. Target Specifications. For use with acoustic guitar. Accurate to 10 cents (musical term) for entire range of guitar pitches Easy to read output LED display. Background - Musical terms.

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Electronic Guitar Tuner

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  1. Electronic Guitar Tuner K. Wettstein A. Wunderlich Senior Design Project Team 45 May 3, 1999

  2. Target Specifications • For use with acoustic guitar. • Accurate to 10 cents (musical term) for entire range of guitar pitches • Easy to read output LED display

  3. Background - Musical terms • 1 octave = 12 pitches • octaves are numbered (lowest to highest) according to range of piano. • 12 pitches: A, A#, B, C, C#, D, D#, E, F, F#, G, G# • 100 cents defined between each pitch

  4. Background - Guitar • Acoustic guitar ranges from E2 (pitch E in piano’s second octave) to C#6. • Plucked string: Fundamental frequency and harmonics • Guitar Spectrum: fundamental frequency has lower power than some higher harmonics. • Lower frequencies have more power in harmonics than higher frequencies. • Demonstrates acoustic non-linearity of string

  5. Guitar Frequency Spectrum

  6. Background:Frequency-Pitch Conversions • Frequency and musical pitch are related on a logarithmic scale: f(octave, pitch) = 16.352 * 2octave + pitch/12 or octave + pitch/12=log2(16.352/frequency) where pitch has values 0-11, starting with C. • cents are represented by the first two decimal places of the pitch value.

  7. Design: Block Diagram • 3 main components: input, DSP, output

  8. Design: Input • Microphone to receive signal • Possibilities: dynamic, condenser, pressure gradient microphone styles • Decision: dynamic • Why? Frequency response and range, availability • Amplifier: To increase microphone amplitude (output Vpp ~ 5-10mV) • op-amp with gain of 100

  9. Design: Digital Signal Processor • Motorola 56302 DSP Evaluation Board • DSP board provides: • analog-to-digital conversion • Fast Fourier Transform (FFT) of signal • lookup tables for frequency conversion to pitch and cents • digital output to LED display

  10. Design: Digital Signal Processor DSP Algorithm 1.) Ready State for continuous, real-time system • check input amplitude • below threshold, stay in ready state • above threshold, proceed to FFT 2.) Take 1024 sample FFT. Store squared magnitudes in memory. FOR MORE INFO... See Handout for flowchart, ‘DSP Algorithm.’

  11. Design: Digital Signal Processor DSP Algorithm…cont. 3.) Start with ninth index, compare magnitudes to a new threshold, which is set above the level of the noise. 4.) Find first peak in FFT data. This corresponds to the fundamental frequency. 5.) Store this index value, use it for pitch and cents lookup tables.

  12. Design: Digital Signal Processor DSP Algorithm…cont. 6.) Write corresponding values to the Data register for Port B. 7.) Port B outputs values to display.

  13. Design: Output • Digital high/low values from Port B of DSP board • Output display: • hexidecimal display for note letters • 1 LED indicating a sharp • 10 LEDs: 5 corresponding to sharpness in units of 10 cents, 5 corresponding to flatness

  14. Verification • Test signals (pure sine and square waves) from function generator. • Tested final circuit with guitar and compared output to commercial guitar tuner. • Verified correct identification of peak from memory contents.

  15. Design Cost Parts cost: Item:Cost: Motorola DSP + Eval. $165.00 Amplifier $2.00 11 LED's $5.00 Hexadecimal Display $2.00 Microphone $120.00 Misc. Comp. $2.00 Total Parts: $296.00 Labor: $3600.00 Complete Cost: $3,896.00

  16. Summary • Designed and implemented tuner. • Accurate within approximately 10 cents. • Accuracy could be increased by taking longer FFT. • Lower sampling rate • Easily Marketable

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