Audio visual system principles #1
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The document explains the principles of audio visual systems, focusing on sound waves as mechanical vibrations that travel through different mediums, with characteristics such as frequency and amplitude. It covers the functionality of the human ear in detecting sound, the speed of sound in various materials, and the fundamental concepts of acoustics including wave propagation and the effects of different types of waves. Additionally, it discusses voice frequency in telephony, the audio chain in sound systems, and room acoustical design considerations.
Audio visual system principles #1
- 1. AUDIO VISUAL SYSTEM PRINCIPLES 1: AUDIO SIGNALS
- 2. THE NATURE OF A SOUND WAVE Sound is a mechanical wave which results from the back and forth vibration of the particles of the medium through which the sound wave is moving.
- 3. THE NATURE OF A SOUND WAVE If there wasn't any air, we wouldn't be able to hear sounds. There's no sound in space. We hear sounds because our ears are sensitive to these pressure waves. the human ear is capable of detecting sound waves with a wide range of frequencies, ranging between approximately 20 Hz to 20, 000 Hz. frequency below the audible range of hearing (i.e., less than 20 Hz) is known as an infrasound. any sound with a frequency above the audible range of hearing (i.e., more than 20,000 Hz) is known as an ultrasound.
- 4. THE NATURE OF A SOUND WAVE Dogs can detect frequencies as low as approximately 50 Hz and as high as 45,000 Hz. Cats can detect frequencies as low as approximately 45 Hz and as high as 85,000 Hz. Dolphins can detect frequencies as high as 200,000 Hz.
- 5. SPEED OF SOUND The speed of sound depends on the medium through which the waves are passing. the speed of sound is approximately 343 m/s (1,230 km/h; 767 mph). In fresh water, also at 20 °C, the speed of sound is approximately 1,482 m/s (5,335 km/h; 3,315 mph). In steel, the speed of sound is about 5,960 m/s (21,460 km/h; 13,330 mph)
- 6. ELECTROMAGNETIC SPECTRUM Sound waves are not electromagnetic radiation. At the lower end of the electromagnetic spectrum, about 20 Hz to about 20 kHz, are frequencies that might be considered in the audio range. However, electromagnetic waves cannot be directly perceived by human ears. Sound waves are the oscillating compression of molecules. To be heard, electromagnetic radiation must be converted to pressure waves of the fluid in which the ear is located (whether the fluid is air, water or something else).
- 7. Legend: γ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme-ultraviolet NUV = Near-ultraviolet Visible light (colored bands) NIR = Near-infrared MIR = Moderate-infrared FIR = Far-infrared EHF = Extremely high frequency (microwaves) SHF = Super-high frequency (microwaves) UHF = Ultrahigh frequency (radio waves) VHF = Very high frequency (radio) HF = High frequency (radio) MF = Medium frequency (radio) LF = Low frequency (radio) VLF = Very low frequency (radio) VF = Voice frequency ULF = Ultra-low frequency (radio) SLF = Super-low frequency (radio) ELF = Extremely low frequency(radio) ELECTROMAGNETIC SPECTRUM
- 8. VOICE FREQUENCY A voice frequency (VF) or voice band is one of the frequencies, within part of the audio range, that is used for the transmission of speech. In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz. It is for this reason that the ultra low frequency band of the electromagnetic spectrum between 300 and 3000 Hz is also referred to as voice frequency, being the electromagnetic energy that represents acoustic energy at baseband. The bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, allowing a sampling rate of 8 kHz to be used as the basis of the pulse code modulation system used for the digital PSTN. As Per the NY Quist–Shannon sampling theorem, the sampling frequency (8kHz) must be at least twice the voice frequency (4kHz) for effective reconstruction of the voice signal.
- 9. VOICE FREQUENCY The voiced speech of a typical adult male will have a fundamental frequency from 85 to 180 Hz, and that of a typical adult female from 165 to 255 Hz Thus, the fundamental frequency of most speech falls below the bottom of the "voice frequency" band as defined above. However, enough of the harmonic series will be present for the missing fundamental to create the impression of hearing the fundamental tone.
- 10. HEARING FUNCTION Sound waves travel through the outer ear, are modulated by the middle ear, and are transmitted to the vestibulocochlear nerve in the inner ear. This nerve transmits information to the temporal lobe of the brain, where it is registered as sound. The ear is filled with three type of fluid that helps the ear to focus the sound, damping the noise & decreases the receptivity of high frequency noise. Sound that travels through the outer ear impacts on the (ear drum), and causes it to vibrate.
- 11. HEARING FUNCTION The pinna, the outer part of the ear, serves to "catch" the sound waves. Your outer ear is pointed forward and it has a number of curves. This structure helps you determine the direction of a sound. Your brain determines the horizontal position of a sound by comparing the information coming from your two ears. If the sound is to your left, it will arrive at your left ear a little bit sooner than it arrives at your right ear. It will also be a little bit louder in your left ear than your right ear.
- 12. HEARING FUNCTION Once the sound waves travel into the ear canal, they vibrate the eardrum. The eardrum is a thin, cone-shaped piece of skin, about 10 millimeters (0.4 inches) wide. It is positioned between the ear canal and the middle ear. The cochlea is by far the most complex part of the ear. Its job is to take the physical vibrations caused by the sound wave and translate them into electrical information the brain can recognize as distinct sound. The eardrum is rigid, and very sensitive. Even the slightest air-pressure fluctuations will move it back and forth. It is attached to the tensor tympani muscle, which constantly pulls it inward. This keeps the entire membrane taut so it will vibrate no matter which part of it is hit by a sound wave.
- 13. WAVE PROPAGATION Sound travels as waves with two physical characteristics: amplitude, which is volume or loudness; and frequency, which is pitch. Amplitude is the height of a sound wave. Frequency represents how often a sound wave goes through a full cycle. As a sound wave travels across distance, the amplitude decreases. This is why we can't hear a quiet whisper across a room.
- 14. SOUND PRESSURE LEVEL Sound pressure is defined as the difference between the average local pressure of the medium outside of the sound wave in which it is traveling through (at a given point and a given time).
- 15. SOUND PRESSURE LEVEL (SPL) • All loudspeaker data sheets should quote the sound pressure level of the loudspeaker measured in decibels (dB). • This is the sensitivity of the loudspeaker at a distance of 1 meter with a speaker input level of 1 watt. • The basic rule is that each time the power input to the loudspeaker is doubled the output level is increased by 3 dB. For example, a loudspeaker having an SPL of 90 dB (for 1W/1M) will have an output of 93 dB for 2 watts, 96 dB for 4 watts etc.
- 16. AUDIO CHAIN Like any other type of systems; the audio system consist of: Input sources • Microphones • DVD • Cassette players • Discussion system Audio processing • Mixers • distribution • Limiters • Filters. Output audio signal • Line level audio signal • Microphone level audio signal. • Powered output audio signal.
- 17. We will show in glance some items from the audio chain
- 18. AUDIO CHAIN – INPUT STAGE The input stage could be any of the following signal types or combined. • Microphone level signal. • Line level signal.
- 19. AUDIO CHAIN – INPUT STAGE Line level is a term used to denote the strength of an audio signal used to transmit analog sound information between audio components such as CD and DVD players, TVs, audio amplifiers, and mixing consoles.
- 20. LINE LEVEL SIGNAL TO MICROPHONE INPUT ADAPTER Sometimes there is need to convert line level signals to such signal that it can be connected to microphone input. Because the line level signals are typically in range of 0.5….2V and the microphone signals are in mill volt range, quite much attenuation is needed to match the signal levels. This means that typically you will need 40-50 dB of attenuation
- 21. The attenuation of the circuit is determined by equation: attenuation (in dB) = 20 * log10 ( (R1 + R2) / R2 ) Equations to calculate different value attenuations R1 = ((Z1 + Z2)* 0.994 + (Z1 - Z2))/4 R2 = ((Z1 + Z2)* 0.994 - (Z1 - Z2))/4 R3 = (Z1 + Z2) / attenuation
- 22. DAMPING OF SOUND LEVEL WITH DISTANCE Sound waves level are inverse proportional to the distance.
- 23. MAXIMUM POWER THEOREM the maximum power (transfer) theorem states that, to obtain maximum external power from a source with a finite internal resistance. the resistance of the load must be made the same as that of the source If the resistance of the load is made larger than the resistance of the source, then efficiency is higher, since most of the power is generated in the load, but the overall power is lower since the total circuit resistance goes up. If the internal impedance is made larger than the load then most of the power ends up being dissipated in the source, and although the total power dissipated is higher, due to a lower circuit resistance, it turns out that the amount dissipated in the load is reduced.
- 24. ACOUSTICS Acoustics and noise:- The scientific study of the propagation, absorption, and reflection of sound waves is called acoustics. Noise is a term often used to refer to an unwanted sound. In science and engineering, noise is an undesirable component that obscures a wanted signal. Fundamental concepts of acoustics:- The study of acoustics revolves around the generation, propagation and reception of mechanical waves and vibrations. Cause Generating mechanism (transduction) Acoustic wave propagation Reception (transduction) Effect
- 25. ACOUSTICS The steps shown in the diagram can be found in any acoustical event or process. The central stage in the acoustical process is wave propagation. This falls within the domain of physical acoustics. In fluids, sound propagates primarily as a pressure wave. In solids, mechanical waves can take many forms including longitudinal waves, transverse waves and surface waves. Acoustics looks first at the pressure levels and frequencies in the sound wave. Transduction processes are also of special importance. Cause Generating mechanism (transduction) Acoustic wave propagation Reception (transduction) Effect
- 26. ACOUSTICS Longitudinal wave:- also known as "l-waves", are waves in which the displacement of the medium is in the same direction as, or the opposite direction to, the direction of travel of the wave. Cause Generating mechanism (transduction) Acoustic wave propagation Reception (transduction) Effect
- 27. ACOUSTICS transverse wave :- is a moving wave that consists of oscillations occurring perpendicular (or right angled) to the direction of energy transfer. If a transverse wave is moving in the positive x-direction, its oscillations are in up and down directions that lie in the y–z plane. Cause Generating mechanism (transduction) Acoustic wave propagation Reception (transduction) Effect Light is an example of a transverse wave. the displacement of the medium is perpendicular to the direction of propagation of the wave. A ripple in a pond and a wave on a string are easily visualized as transverse waves.
- 29. ACOUSTICS surface wave :- is a mechanical wave that propagates along the interface between differing media. A surface wave can also be an electromagnetic wave guided by a refractive index gradient. In radio transmission, a ground wave is a surface wave that propagates close to the surface of the Earth. Cause Generating mechanism (transduction) Acoustic wave propagation Reception (transduction) Effect
- 30. ACOUSTICS standing wave :- is a wave that remains in a constant position. This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling in opposite directions. Cause Generating mechanism (transduction) Acoustic wave propagation Reception (transduction) Effect
- 31. ACOUSTICS In order to do acoustic measurements, you have to know how to measure and also what to measure. A precondition for an optimum room-acoustical design of auditoriums and concert halls is the very early coordination in the planning phase. The basis here is the establishment of the room's primary structure according to its intended use (room shape, volume, topography of the spectators’ and the platform areas). The secondary structure that decides the design of the details on walls and ceilings as well as their acoustic effectiveness has to be worked out on this basis. Cause Generating mechanism (transduction) Acoustic wave propagation Reception (transduction) Effect
- 32. ACOUSTICS In principle, the room-acoustical quality criteria can be subdivided into time and energy criteria. The main type of use – speech or music, then determines the recommendations for the guide values to be targeted. With multi-purpose halls (without available variable measures for changing the acoustics), a compromise is required that should orient itself to the main type of use. Cause Generating mechanism (transduction) Acoustic wave propagation Reception (transduction) Effect
- 33. ACOUSTICS The Reverberation Times :- The reverberation time RT is the time that passes after an acoustic source in a room has been turned off until the mean steady-state sound-energy density w(t) has decreased to 1/1,000,000 of the initial value w0 or until the sound pressure has decayed to 1/1,000, i.e. by 60 dB: Cause Generating mechanism (transduction) Acoustic wave propagation Reception (transduction) Effect