SPECIFICATIONS OF MICROPHONE
The selection of microphones is done by using their characteristics. The characteristics of a microphone are explained as follows:
1. Sensitivity: It is defined as the electrical output in volts for the input sound pressure of 1 microbar at 1 kHz. Sensitivity should be high for a good microphone.
2. Signal Noise Ratio: It is the ratio of output in the presence of sound to the output in the absence of sound. It is expressed in decibel (dB). For a good microphone signal-to-noise ratio should be high.
S = 20 log N output in the presence of sound output in the absence of sound
3. Frequency Response: The frequency response of a microphone is a measure of its ability to faithfully convert different acoustical frequencies into alternating current. This is a plot drawn between the frequency and output of the microphone. The frequency response must be flat for a good microphone.
4. Distortion: The variation in output from the input is known as distortion. The distortion may be
(a) Non-linear distortion.
(b) Phase distortion.
5. Directional Pattern or Directivity: Directivity indicates the direction from which the microphone picks up the sound signal. It is indicated by curved patterns. Different directional patterns are:
(a) Omni directional.
(b) Bidirectional or figure of eight.
(c) Cardioid or heart-shaped.
Output Impedance: The output impedance of the microphone is represented in ohms. This is a very important characteristic because the output impedance of the microphone should match the input impedance of the device converted to the microphone.
SPECIFICATIONS OF LOUDSPEAKER
1. Efficiency (Sensitivity).
2. Signal to Noise ratio.
3. Frequency response.
4. Directivity.
5. Input impedance.
6. Power handling capability.
7. Distortion.
8. Physical factors.
FREQUENCY RESPONSE AND EQUALIZATION
Frequency Response: The graph between the gain and frequency of an audio system is known as frequency response.
Frequency response can be obtained for amplifiers microphones, loud speakers, etc.,
Equalization: Equalization is the process of improving the (S/N) ratio by modifying the frequency characteristics before recording and neutralizing that modification in playback amplifiers.
Equalization is achieved by using pre-emphasis and de-emphasis circuits. Losses at low frequency and high frequency. To obtain a good frequency response to equalize (or) compensate for these low-frequency and high-frequency signals by using an equalizer.
High-frequency loss is corrected during the recording process and low-frequency loss is corrected in the playback circuits. Pre-emphasis the low-intensity sounds before recording and de-emphasizing in the playback circuit is known as "equalization".
To increase the magnitude of low-intensity sound by using a pre-emphasis circuit at a recording circuit and the corresponding cut at the playback circuit by using a de-emphasis circuit.
CONCEPT OF HIGHFIELDITY(HI-FI)
•Hi-Fi stands for high-fidelity. In audio systems, it is used to indicate faithful reproduction of sound.
• When the sound is reproduced with a similar to the original or live sound, it can be said to be high fidelity or simply Hi-Fi.
• High-fidelity sound can be obtained from the recorded stereo tape or in a live system from the microphones, the stereo signal is fed to two independent channels for amplification of the amplifiers, an equalizer for giving that frequency response with little distortion.
• For Hi-Fi, the loudspeakers consist of
Woofer: 16 Hz - 500 Hz for low frequency range.
Squawker: 500 Hz - 5 KHz for mid-frequency range
Tweeter: 5 kHz - 20 kHz for high frequency range
Characteristics of Hi-Fi System
1. Flat frequency response of the amplifiers within 16 Hz - 20 kHz.
2. Noise level should be 50 dB below.
3. (S/N) ratio should be more than 50 dB.
4. Amplitude and phase distortions are less.
CONCEPT OF STEREO SYSTEM
Thus In a program (say an orchestra), different sources of sound are placed at different positions on the stage when such a program is amplified and reproduced.
PRINCIPLE OF OPTICAL RECORDING OF SOUND
Sound can be recorded optically by two methods viz: recording on photographic film and recording on compact disc.
Recording on photographic film: The intensity of light from a slit is made to vary in accordance with the sound pressure variations. When this varying light falls on the edge of the main film, a photograph of the varying light intensity is recorded in the form of varying color density or area. This variation of color is in accordance with the variation of light which in turn is in accordance with the sound.
Recording on compact disc: This is done with the help of laser beams, made ON and OFF by digitized audio signals.ary form. Flats and pits make 1s and 0s respectively.
SOUND RECORDING METHODS
1. Disc Recording.
2. Magnetic Recording.
3. Optical Recording.
4. Digital Recording.
OPTICAL RECORDINGS
Recording on Compact Disk :
• The is done with the help of laser beams, made ON and OFF by digitized audio signals.
• These beams fall on the photoresist material on a rotating disc and cause pits of varying width and fixed depth and thus record signals in binary form, flats, and pits making 1s and 0s.
FEATURES OF HOME THEATRE SYSTEM
The basic features of the home theatre system are:
• It recreates the experience of watching a movie in a theatre.
• Listeners can hear different parts of the soundtrack from different places.
• It delivers Hi-fidelity with quality audio
• It produces a low pitch frequency. In other words, the subwoofers produce the bass sound.
CONCEPT OF NOISE REDUCTION BY THE DOLBY SYSTEM
• Dr. Ray Dolby discovered novel system for 10-15 dB improvement in recording, playback tapes. When the strength of signals falls below a predetermined level (say, 40 dB over the noise novel), the circuit boosts the strength before recording.
• All signals that are 40 dB are higher, pass through the Dolby system directly without any change. The lower-level signals pass through the boosting stages which boost these signals by 10-15 dB. Boosting is done before recording.
• Signals in the absence of boosting. after boosting, the noise remains unchanged but, the signal is boosted.
• It indicates that the (S/N) ratio is finally improved.
