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 (1705-535=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 107.9 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