AVE UNIt 1.pptx..........................

It will help in consumer elestronics

1. AUDIO FUNDAMENTALS AND DEVICES

2. CONTENTS Basic characteristics of sound signal-sound intensity, level and loudness, pitch, frequency response, fidelity, linearity and reverberation Sound recording ,optical recording, stereophony and multichannel sound,MP3 standard, dolby NR recording system Introduction to amplifiers, types –mono, stereo, difference between stereo and mono amplifier Public address system-necessity , working , block diagram of Hi- Fi amplifiers, controls available on it and their function,graphic equalizer- concept , circuit diagram and its operation(5 point circuit diagram)

3. Microphone- types, wireless microphone Types of speaker-woofer, midrange, tweeter, cross over network circuit and its function

4. BASIC CHARACTERISTICS OF SOUND SIGNAL Sound is a longitudinal wave motion consisting of train of compression and rarefactions travelling in a medium. When sound waves strike ear drum ,they are converted to electrical signals. the auditory nerve carry these signals to brain and interpret them ,this is what we call sound. Being wave motion sound has all characteristics of wave ; amplitude, frequency , velocity , wavelength and phase

5. AMPLITUDE- Intensity of compressions and rarefactions produced in medium. FREQUENCY- number of successive compressions and rarefactions occuring in one second and expressed in Hertz. audible frequency range 16Hz to 20kHz TIME PERIOD- Time taken in completing one cycle T=1/f sec

6. VELOCITY- distance travelled in one second, sound waves move in air with a velocity of 344m/s at 20 degree celcius or 332m/s at 0 degree celcius . WAVELENGTH- The length of space travelled by one cycle of variation and is represented in metres V=f λ PHASE- It indicates state of motion at a particular instant relative to some reference expressed in terms of angle.

7. SOUND INTENSITY- Sound waves produce variations of pressure in medium for voice and musical instruments the medium is air, greater the intensity of sound greater will be the compressions and consequent rarefactions . In terms of energy intensity of sound wave is defined as the average rate of flow of sound energy through cross sectional area of one square meter at right angles to the direction of motion. Intensity of sound energy is represented in Watts/m and is proportional to square of amplitude, generally indicated in dB.

8. LEVEL AND LOUDNESS- Loudness is a subjective effect , and it depends on how and individual feels it . Here output is represented not in dB but in dBA . FREQUENCY OF SOUND WAVES- Audible frequency range 16Hz to 20kHz 2 factors that determine frequency range are intelligibilty and energy.

9. BANDWIDTH OF SOUND WAVES- For telephonic speech 300 to 3400 Hz. For normal program 80 to 5000Hz. For high fidelity 40 to 15000Hz. It has been established that high frequencies contain low energy but high intelligibility and low frequencies contain high energy but low intelligibility . The frequencies of women’s voices are higher than those of men . Interval is the ratio of 2 frequencies and interval of 1:2is called one Octave. Harmonics are integer multiplies of fundamental frequencies Frequencies higher than fundamental frequencies are called overtones thus overtones include harmonics also.

10. PITCH- It is a characteristic of sound mainly related to frequency. In pure tones without harmonics it represents frequency alone but with harmonics it is related to intensity also in addition to frequency. FIDELITY- The word fideilty means faithfulness. In audio systems it is used to indicate faithful reproduction of sound.

11. LINEARITY - Every acoustic system is linear to high degree. Linearity is represented as a straight line , here linearity of sound means that these are sounds are always going to be the same once you have used them . A linear system cannot change the frequency of original partial and wont produce new partial during the process.

12. REVERBERATION- Sound being a motion ,suffers reflection ,refraction ,diffraction and absorption in accordance with the specified rules as for any wave motion . Due to multiple reflections from walls, ceilings,floors,etc. the sound in an enclosure fades away only gradually after the source of sound stops ,this continuing echo is called reverberation.

13. SOUND RECORDING OPTICAL RECORDING- 2 types- recording on photographic film recording on compact disc Recording on photographic film- done by converting audio signals into variations of light intensity falling on film Recording on compact disc- done with the help of laser beams made on and off by digitized audio signal. these beams fall on a photo resistant material on a rotating disc and cause pits of varying width and fixed depth and thus records signals in binary form.

14. METHODS OF OPTICAL RECORDING- Variable density method

15. Variable area method

16. STEREOPHONY The word stereophony is derived from 2 greek words stereos and phone meaning solid and sound respectively. Thus stereophony means solid sounds or 3 dimensional sounds.

17. MP3 STANDARDS MP3 is a coding format for digital audio . Originally defined as a third audio format of the MPEG-1standard ,it was retained and further extended –defining additional bitrates and support for more audio channels.

18. DOLBY NR RECORDING SYSTEM Dr.Ray Dolby introduced a novel system for providing 10 -15dB improvement in recording and playback tapes. In normal pre-emphasis it is presumed that weak intensity is present only in high frequencies. This is not always the case , all weak signals irrespective of their frequencies need to be emphasized , this difficulty is solved by Dolby. When strength of signal falls below a pre determined level the circuits boost the strength before recording ,all signals which are 40dB or higher pass through dolby system without change , the lower signals pass through boosting stages which boost these signals by 10-15dB. Boosting is done before recording.

19. Required to emphasis (Boost) the low power signal before recording since these signal are more effected by noise. Low power notes are more closer to the noise signal. These signals are pre-emphasized before recording and de-emphasized before playing them back. Pre-emphasis is of 10db to 15db for low power notes. Selected signals are pre-emphasized which are below a predetermined level while above this are passed through dolby system directly. Two types of dolby systems. 1) Dolby A systems. 2) Dolby B systems.

20. MONO AND STEREO AMPLIFIERS Mono amplifier system- Mic : It convert sound waves into electrical signal & send to buffer stage. Buffer stage : It’s function is to provide impedance matching. Power amp : It can provide amplified signal for different sound waves. Loud speaker : It Convert electrical signal into sound signal.

21. STEREOPHONIC AMPLIFIER SYSTEM- Mic : It convert sound waves into electrical signal & send to buffer stage. Power amp : Provide amplified signal for different sound waves. Loud speaker : It Convert electrical signal into sound signal.

22. Advantages : Sound has direction right & left. This system is used for high-fidelity amplification purpose. Disadvantages : Amplitude/frequency/phase distortion is more.

23. PUBLIC AMPLIFIER SYSTEM Amplifier used for addressing the people is known as public address amplifier. Provide sound to long distance without scarifying the original signal / information.

24. Mic : It convert Sound Waves Into Electrical signal. Mixer : It combines all the input& produced output V4=v1+v2+v3. Voltage Amplifier : Amplifies weak signal coming from mixer stage. Power amp : Provide high amplified signal for different sound waves. Loud speaker : It Convert electrical signal into sound signal.

25. Advantages : Minimum noise level For amplification of speech signal frequency response is flat. Gain is constant. Disadvantages : It has the effect of positive feedback which will oscillate the amplifier & will reproduced the distortion.

26. HI-FI AMPLIFIER SYSTEM Amplifier output is similar to original information called HI-FI amplifier Minimum requirement of HI-FI amplifier. Directional sound. It should have minimum frequency & phase distortion. Minimum noise level. Flat frequency.

27. Output from various input sources like disk player or mic are connected to switches. Switches are connected to pre-amplifier whose function is to provide AV=high. Output of pre-amplifier contain more noise to remove these noise we used equalizer. Equalizer consist of different filters like low, medium & high frequency filter .

28. Output of equalizer fed to power amplifier to provide Av =high & Ai=high & fed to crossover network through impedance matching circuit. Output of crossover network contains electrical signal for 60Hz to 15Khz with flat frequency response. One speaker is unable to reproduced equal intensity sound hence, a separate speaker is used for low, medium & high frequency as woofer, midrange & tweeter. Crossover network separate low frequency signal for woofer, medium frequency signal for midrange & high frequency signal for tweeter

29. STEREO AMPLIFIER MONO AMPLIFIER Two dimensional sound Two pre-amplifier used Sound is natural Direction of sound sensed easily Costly Direction sound One pre-amplifier used Lack of naturalness No sense of direction Less costly than stereo DIFFERENCE BETWEEN MONO AND SEREO AMPLIFIER

30. STEREO AMPLIFIER PUBLIC ADDRESS AMPLIFIER Distance increases sound level decreases Noise is more Sensitivity is less Echo effect is more Variation in gain with respect to temperature Less costly They prefer for addressing people for larger area. Minimum noise level Sensitivity is more Echo effect is less It is high power temperature compensated so, variation in gain is minimum Cost is more DIFFERENCE BETWEEN PA AND STEREO AMPLIFIER

31. Controls of Hi- Fi System Microphone gain control. Master gain control (Volume control). Tone control 1. Bass control 2. Treble control

32. Microphone Gain Control- Controls output of microphone. Connected in either pre-amplifiers or mixers. Potentiometers are used for the gain controls. Master Gain Control- Logarithmic potentiometers are used for the gain control which matches logarithmic response of the human ears. Value of resistance is twice that of load.

33. Tone Control Bass Control: • Bass effect will increase if capacitance in series with the signal increases. • Higher the capacitance the value of reactance decreases.

34. Treble Control- High resistance at potentiometer will develop maximum signal across the load and goes on boosting treble. For high value of capacitance value the reactance decreases ( Xc =2*pi* fc )

35. Graphic equalizer- Special type of tone control where audio spectrum is divided into various narrow spectrums. Individual spectrums can be boosted by moving sliders in between +15 db to -15 db.

36. Parameter Woofer Mid Range Tweeter Frequency response 16Hz to 500Hz 500Hz to 5Khz 5Khz to 20Khz Size Large Medium Small Cross over network Used 2 & 3 way system Only 3 way system Used 2 & 3 way system Cost Large Medium Less Uses in Mono / Stereo amplifier. Hi- Fi system Stereo/Hi- Fi system Frequency Passed Low Medium High TYPES OF SPEAKERS-

37. CROSS OVER NETWORKS Necessity of cross over network : To avoid overheating of speaker. To increase overall efficiency. To avoid distorted output when full power is fed to load outside the frequency range.

38. Cross over network (2 way)- Consists of low pass filter connected across woofer and high pass filter connected across tweeter. fc is lower cut off frequency for high pass filter while it is higher cut off frequency for low pass filter

39. MICROPHONE It is a transducer which converts sound pressure variations into electrical signals of same frequency and phase and amplitude in same proportions in pressure variations. Characteristics of mic - Sensitivity , signal to noise ratio,frequency response, distortion, directivity, output impedence .

40. Types of microphones- 3 types- Very low impedence ( Ω to 50 Ω ) Medium impedence (100 to 600 Ω ) High impedence (750k Ω and higher) Types – moving coil, ribbon, crystal, capacitor, carbon microphone.

41. Wireless microphone(radio)- It uses small frequency modulated VHF transmitter of low power . Cable from amplifier to microphone is not needed. The signal received by VHF receiver placed at a suitable distance then amplified and fed to the loud speaker. It is useful in sports for oath taking ceremony.