Audio Technologies

Waveform The image of the oscillation Amplitude= the height or depth of the signal from the time baseline Frequency= number of wave crests that pass a fixed point in a given period of time Phase=half wavelength

Amplitude Modulation amplitude modulation = varying the amplitude of a carrier to create an analog of the original signal; i.e., changing the heights of the signal in relation to the time baseline.

Frequency Modulation Frequency modulation= varying the frequency of a carrier to create an analog of the original signal

Signal Propagation AM and other short wave frequencies, two types of radio waves gets the signal over the horizon from the site of the antenna –Groundwaves –Skywaves: Kennelly-Heavyside layer (called skip). FM and higher use direct waves

AM Radio Channels 117 channels in AM 535 to 1705 with AM signal 10 Khz wide. The extra 10 were added in 1993 for moving existing stations ( =1170 divided by 10=117 channels). a station at 760 KHz transmits a signal from 755 Khz to 765 KHz with the carrier at 760).

AM Channels Class A stations 60 channels operate unlimited schedules on clear channels (10 to 50KW) Class B stations 51 channels unlimited schedules on clear or regional channels (.25 to 50KW)

AM Channels Class C stations 6 local channels (1,000 watts to 250 watts) Class D stations daytime, limited time or low powered. Directional night time (less that 250 watts). Not protected from interference and protect class A & B stations

FM FM has 100 channels from 88 Mhz to 108 Mhz [88.1 to channels 201 to 300] each channel is 200 KHz wide, which is why there are no even FM stations. E.g., WUAL transmits at 91.5 MHz but its signal stretches from 91.4 to 91.6 MHz.

FM Class A Channels FM consists of 20 Class A channels (all zones). –Class A stations effective radiated power (ERP) up to 3,000 watts –antenna HAAT (Height above Average Terrain) of no more than 300 feet. These stations cover about 15 miles.

FM Class B Channels There are 60 Class B (zone I IA) stations that –transmit at 50,000 watts and –500 feet HAAT. –Cover about 30 miles.

FM Class C Stations Class C stations (zones II) –transmit with up to 100,000 watts –HAAT of 2,000 feet. –This normally gives a coverage area of about 60 miles. There are 20 channels at the lowest part of the FM spectrum for nonprofit, noncommercial radio stations

Noncommercial FM There are 20 channels at the lowest part of the FM spectrum for nonprofit, noncommercial radio stations

Ribbon Microphone

Typical Ribbon Microphones RCA BX 44 RCA 77 DX

Dynamic Microphone

Typical Dynamic Microphones Shure SM 57 and E-V 635A

Condenser Microphone

Lavalieres RCA BK 12 A (dynamic) & Beyer Dynamic

Omnidirectional

Uni and Bidirectional

Cardiod

Tape Heads