HARMONIC ANALYSIS OF ACOUSTIC WAVES

Transcription

1 Practical No3 HARMONIC ANALYSIS OF ACOUSTIC WAVES Equipment 1. Analog part: spectrum analyzer, acoustic generator, microphone, headphones. 2. Digital part: PC with sound card, microphone and loudspeaker. Fig. 1 Scheme of front panel of spectrum analyzer Fig. 2 Front panel of spectrum analyzer 1. The switch allows you to keep the last measurement in the analyzer memory 2. Mode switch (instantaneous/maximum measurement). 3. Display of spectrum analyzer. 4. Range switch. 5. Amplification knob. 6. On/off switch. 7. Input jack (for connecting function generator or microphone). Course of the practical Analog analysis 1. Set the signal amplitude potentiometer in a position at which the signal amplitude in the spectrum analyzer (vertical scale) does not exceed 0 db in the whole spectrum of analyzed frequencies. Set the band switch into position "-20 db". CAUTION! Turn the potentiometer WZM of the spectrum analyzer to the left most position. Increase the level of the acoustic signal from the generator until basic tone aliquotes may be observed in the analyzer. 2. Connect the microphone to the spectrum analyzer. Set the band switch into position "MIK" -this setting will make active the potentiometer WZM. Set the potentiometer WZM in a position at which the amplitude of the signal in the spectrum analyzer does not exceed 0 db. Get the acoustic spectrum of four 1

2 vowels: u (example: boot), a (example: far), i (example: need) and ε (example: bed). After sound emission immediately switch the analyzer from pomiar (=measurement) to pamięć (= memory) mode. Present the spectra in the appropriate plots of the report s sheet. CAUTION! When speaking hold your mouth in the long axis of the microphone. 3. Choose a consonant and get its spectrum in a way identical to that described in 2. Present the spectrum the appropriate plot of the report s sheet. Digital analysis 1. Turn on the PC. Run the program Analiza by double clicking its icon present at the computer s desktop. Click OK at the bottom of the welcome screen. 2. Below figure presents the English translation of the Polish program options 3. To record the sound choose the option Sounds/Record. In the middle of the screen new panel will appear: To start recording click Record, to stop click Stop. To finish the recording procedure and return to the main screen click Quit. While recording keep microphone not very close to your mouth and speak not too loud. The maximal amplitude of the recorded sound could not exceed the borders of the window in which sound is displayed. The recording should last only few second. Otherwise the computer will spend too much time analyzing the recorded sound. 4. Analyze sounds u, a, i, ε and a chosen consonant by choosing the option Analysis/Fourier transform. Put the results (frequencies of the harmonics and amplitude ratios) into the appropriate table. Plot acoustic pressure against time for the vowel u in the frame in the report s sheet. 2

3 5. To synthesize a sound choose option Synthesis/Sound data. A new panel will appear in which Częstotliwość is frequency (basic) and Stosunek amplitud is amplitude ratio. Start synthesis with the vowel u. After entering data for synthesis click on Gotowe button (which means ready). If during the entering sound data an error communicate will appear click OK and exchange dots for comas (or opposite) in the decimal numbers. Plot acoustic pressure against time for the synthesized vowel u in the frame in the report s sheet. Required theoretical knowledge 1. The speech organ, the ear and their structure. 2. Acoustic waves, objective (physical) and subjective properties of sound. Loudness, loudness level. 3. Fourier theorem. Fourier analysis. Sound timbre. 4. Helmholtz and Bekesy theory of hearing. 3

4 Wrocław Medical University Department of Biophysics... Practical No 3 Harmonic analysis of acoustic waves Tutor s signature... Faculty: Group: Students names Date: Grade: Part I the analog analysis [db] Vowel u [db] Vowel a k 2k 4k 8k 16k k 2k 4k 8k 16k [db] Vowel i [db] Vowel e k 2k 4k 8k 16k Hz k 2k 4k 8k 16k [db] Consonant k 2k 4k 8k 16k 4

5 Part II the digital analysis Sound u a i e consonant Frequency Fourier spectrum of chosen sounds Amplitude ratio 2:1 3:1 4:1 5:1 6:1 7:1 8:1 9:1 10:1 Time dependency of acoustic pressure for vowel u Student:... Natural sound Synthesized sound Student:... Natural sound Synthesized sound 5