PHYS 1240 Sound and Music Professor John Price. Cell Phones off Laptops closed Clickers on Transporter energized

Transcription

1 PHYS 1240 Sound and Music Professor John Price Cell Phones off Laptops closed Clickers on Transporter energized

2 Electronics and Music Introduction Analog versus Digital Live Sound Sound Recording Voltage and Current Coulomb Force and Lorentz Force Magnetic Transducers moving-coil loudspeaker dynamic microphone guitar pick-up phonograph cartridge Electrostatic Transducers condenser microphone electret microphone piezo pick-up electrostatic loudspeaker

3 Analog Signals Any physical quantity that varies continuously as a function of time and represents some kind of information. acoustic pressure time position time voltage time Example: sound pressure moves a microphone diaphragm and the microphone generates a voltage signal.

4 Digital Signals A sequence of numbers that gives an approximate representation of an analog signal. Analog Signal voltage time Sampled Analog Signal voltage time ττ = sampling time (s) 1/ττ = sampling rate (Hz) Sampled and Digitized Analog Signal (8-bits in this example) bit binary numbers range from 0 to 255 or -128 to bit binary numbers range from 0 to or to

5 Binary Numbers 4-bit binary numbers range from 0 to 15 or -8 to +7 8-bit binary numbers range from 0 to 255 or -128 to bit binary numbers range from 0 to or to example: 4-bits count backwards

6 Bit Resolution and Sampling Rate

7 25-1 Binary counting: 000, 001, 010, What comes next? A) 100 B) 110 C) 011 D) 101 E) 111

8 25-2 How many different numbers can I represent with 6 bits? A) 6 B) 8 C) 16 D) 32 E) 64

9 Calculating bit rates Example: CD quality or.wav file samples/second x 16 bits/sample x 2 channels = 1,411,200 bits/second or about 1.4 megabits/second, written as 1.4 Mb/s or 1.4 Mbps Calculating files sizes Example: 30 minute long CD or.wav file 1.4 megabits/second x 60 seconds/minute x 30 minutes = 2.52 Gigabits = 2.52 Gb 8 bits = 1 byte divide by 8 bits/byte 315 Mbyte

10 Nyquist: 0 to Hz Calculating bit rates Example: CD quality or.wav file samples/second x 16 bits/sample x 2 channels = 1,411,200 bits/second or about 1.4 megabits/second, written as 1.4 Mb/s or 1.4 Mbps Calculating files sizes Example: 30 minute long CD or.wav file 1.4 megabits/second x 60 seconds/minute x 30 minutes = 2.52 Gigabits = 2.52 Gb 8 bits = 1 byte divide by 8 bits/byte 315 Mbyte

11 25-3 Suppose I record 8 channels at 8-bit resolution using a 10 khz sampling rate. What is the bit rate? A) 6.32 Mbps B) 2.84 Mbps C) 1.56 Mbps D) 0.79 Mbps E) 0.64 Mbps

12 25-4 Suppose I record 8 channels at 8-bit resolution using a 10 khz sampling rate, and I continue for 10 minutes. What is the file size? A) 48 Mbyte B) 32 Mbyte C) 27 Mbyte D) 15 Mbyte E) 5.6 Mbyte

13 Live Sound Transducer Amplifier Processing Amplifier Loudspeakers Microphones Electric Guitars Keyboard Synthesizers Sequencers Scratching Filters and Equalization Reverb Compression Wah Wah Mixing

14 Live Sound Analog Transducer Amplifier Processing Amplifier Loudspeakers Microphones Electric Guitars Keyboard Synthesizers Sequencers Scratching Analog or Digital Filters and Equalization Reverb Compression Wah Wah Mixing Analog or Digital Examples: Route 66, two versions Amy Winehouse at Glastonbury Spring Reverb

15 Sound Recording Transducer Amplifier Storage Storage Amplifier Loudspeaker Grooves Magnetic tape Magnetic disc Optical disks Semiconductor memory Analog Analog or Digital Digital Digital Digital

16 Cylindrical Phonogram (Thomas Edison 1877 )

17 Edison Phonograph 1879 YouTube videos: Original player Modern recording Stroh violin

18 Acoustic Recording Session ca. 1920

19 Audio Recording Timeline Major consumer storage formats in blue 1877 Edison invents the cylinder recorder/player 1887 Berliner invents the flat-disc gramophone 1888 Edison introduces motor-driven phonograph 1906 DeForest invents the vacuum triode inch 78 rpm electrically-recorded disks 1935 First plastic-based magnetic tape 1948 Long-playing microgroove 33-1/3 rpm vinyl disks 1956 IBM introduces the magnetic hard disk 1957 Stereo 33-1/3 rpm disks 1963 Philips introduces the cassette tape 1966 First commercial semiconductor memory devices 1980 Digital multi-track tape recorder 1981 Philips introduces the optical compact disk (CD) 2001 Apple introduces the ipod (uses digital magnetic disk) 2005 Apple introduces the ipod Nano with semiconductor memory

20 78-rpm Records 4-5 minutes per side thick and fragile stylus moved horizontally

21 33-1/3 rpm Microgroove Records up to 30 minutes per side had an upgrade path to stereo used magnetic or piezo cartridges

22 Audio Compact Disks (optical disks)

23 Audio Compact Disks (optical disks) 750 Mbytes 75 minutes of audio

24 Semiconductor Memory: Flash type Charge on the floating gate attracts or repels electrons in the channel silicon channel

25 Electronics and Music Introduction Analog versus Digital Live Sound Sound Recording Voltage and Current Coulomb Force and Lorentz Force Magnetic Transducers moving-coil loudspeaker dynamic microphone guitar pick-up phonograph cartridge Electrostatic Transducers condenser microphone electret microphone piezo pick-up electrostatic loudspeaker

26 Elements of Electronics: Voltage and Current Matter is normally electrically neutral because there are equal numbers of negatively charged electrons and positively charged nuclei. The Si unit of charge is the Coulomb (C) The charge of an electron is very small, only C

27 Elements of Electronics: Voltage and Current An electrical current is the flow of charge In an electrical insulator, charge cannot hop from one atom to another In an electrical conductor, charge can hop from one atom to another The SI unit of current is the Ampere (A). 1 Ampere = 1 Coulomb/second

28 Elements of Electronics: Voltage and Current In a metal, the negative electrons can flow and the positive nuclei are fixed. Since electrons are negatively charge, when the current flows to the right, the electrons flow to the left. electrons current

29 25-5 Which material is insulating? A) iron B) glass C) copper D) aluminum E) more than one of the above

30 25-6 Which material is conducting? A) rubber B) glass C) copper D) salt water E) more than one of the above

31 25-6 Which material is conducting? A) rubber B) glass C) copper D) salt water E) more than one of the above electronic conductor ionic conductor

32 Elements of Electronics: Voltage and Current Voltage is analogous to pressure in a pipe filled with water. Voltage differences make charge flow (creating a current) just as pressure differences make water flow. higher pressure pipe water flow lower pressure higher voltage wire charge flow = current lower voltage

33 Elements of Electronics: Voltage and Current Most conductors obey Ohm s Law. The resistance R measures how much the conductor resists flow of current I when a voltage V is applied. voltage in Volts (V) II = VV RR current in Amperes (A) resistance in Ohms ( Ω)

34 I 25-7 V R Suppose the voltage is 6 V and the resistance is 10 Ω. What is the current? a) 6 A b) 0.16 Α c) 0. 6 Α d) 1.6 Α

35 I 25-8 V R Suppose the current is 3 A and the voltage is 6 V. What is the resistance? a) 3 Ω b) 2 Ω c) 1/2 Ω d) 1/3 Ω

36 I 25-9 V R Suppose the current is 3 ma and the voltage is 6 V. What it the resistance? a) 3000 Ω b) 2 kω c) 500 mω d) 333 µω

37 I V R Suppose the voltage is 6 V and the resistance is 1 MΩ. What is the current? a) 6 ma b) 6 µα c) 1.6 ma d) 1.6 MA

38 Electronics and Music Introduction Analog versus Digital Live Sound Sound Recording Voltage and Current Coulomb Force and Lorentz Force Magnetic Transducers moving-coil loudspeaker dynamic microphone guitar pick-up phonograph cartridge Electrostatic Transducers condenser microphone electret microphone piezo pick-up electrostatic loudspeaker

39 Electrostatic Forces QQ 1 QQ 2 r FF = kk QQ 1QQ 2 rr 2 Coulomb s Law Force is attractive between charges of opposite sign. Force is repulsive between charges of the same sign. Coulomb Constant kk = Nm 2 /C 2 UCLA demo on Youtube

40 nc 2 nc 0.5 m Suppose I set up two charges as shown above. Now I change the distance between them to 1.0 m. Which statement is true? A) The force is repulsive B) The force become half as strong C) The force becomes twice as strong D) The force becomes four times stronger F) The force becomes four times weaker.

41 nc 2 nc 0.5 m Suppose I set up two charges as shown above. Now I change the charge on the right to -1 nc. Which statement is true? A) The force is repulsive B) The force become half as strong C) The force becomes twice as strong D) The force becomes four times stronger F) The force becomes four times weaker.

42 Magnetic Fields BB The magnetic field has both magnitude and direction. Magnetic fields are created by currents, either in wires or atomic currents in magnetic materials. The equation describing how currents create magnetic fields is called Ampere s law. Field visualization Demo Peter Fletcher on Youtube (jump to 5:50)

43 Magnetic Force on a Charge BB QQ FF vv FF = QQ vv BB FF = QQQQQQ Vector Lorentz force for a charge moving in a magnetic field Magnitude of the Lorentz force when v and B are perpendicular Lorentz force demo

44 Magnetic Force on a Wire BB wire length LL FF II FF = LL II BB FF = LLLLLL Vector Lorentz force on a currentcarrying wire Magnitude of the Lorentz force on a current carrying wire force (N) current (A) length (m) magnetic field (T)

45 Magnetic Force on a Wire BB II What is the direction of the Lorentz force? A) Out of the plane of the drawing B) C) D) E) jumping wire demo

46 Electronics and Music Introduction Analog versus Digital Live Sound Sound Recording Voltage and Current Coulomb Force and Lorentz Force Magnetic Transducers moving-coil loudspeaker dynamic microphone guitar pick-up phonograph cartridge Electrostatic Transducers condenser microphone electret microphone piezo pick-up electrostatic loudspeaker

47 Moving-Coil Loudspeaker Rice and Kellog, General Electric, 1924

48 Radial field makes an axial force F B I Loudspeaker formula: coil radius (m) FF = 2ππππππππππ current (A) magnetic field (T) # of turns

49 25-15 Loudspeaker formula FF = 2ππππππππππ Suppose the magnetic field in the coil gap is 0.4 T, the coil has 40 turns and the coil radius is 1 cm. What is the axial magnetic force when 1 A flows through the coil? a) 6.3 N b) 2.5 N c) 1.0 N d) N e) 0.45 N

50 Dynamic Microphone Moving a coil in a magnetic field creates a voltage

51 Phonograph cartridge coils moving magnet stylus Moving magnet changes the magnetic field through two coils and creates two (stereo) voltages.

52 Phonograph cartridge audio-technica AT440MLa Moving magnet changes the magnetic field through two coils and creates two (stereo) voltages.

53 Guitar Pick-up Moving string changes the magnetic field through the coil and creates a voltage.

54 Electronics and Music Introduction Analog versus Digital Live Sound Sound Recording Voltage and Current Coulomb Force and Lorentz Force Magnetic Transducers moving-coil loudspeaker dynamic microphone guitar pick-up phonograph cartridge Electrostatic Transducers condenser microphone electret microphone piezo pick-up electrostatic loudspeaker

55 Capacitance

56 Capacitance Transient +Q -Q

57 Capacitance Transient charge in Coulombs (C) voltage in Volts (V) VV = QQ CC +Q -Q capacitance in Farads (F)

58 Parallel-plate Capacitor a constant area (m 2) CC = εε 0AA dd gap (m) capacitance in Farads (F)

59 25-16 Suppose charges +Q and Q are distributed over opposite plates of a parallel-plate capacitor with area A and gap d. What happens to the voltage across the capacitor if I reduce d to d/2 without changing the charges? a) the voltage is multiplied by 2 b) the voltage is multiplied by 4 c) the voltage is divided by 2 d) the voltage does not change

60 Condenser Microphone

61 Electret Microphone Cell West and Sessler, Bell Labs, 1962 Electret Thin Film a charged waxy material high voltage not required

62

63 Piezoelectric pick-up

64 Electrostatic Loudspeaker NPS summary video

65 Supplemental Slides