SOUND–MUSIC-MIDI-SPEECH

1. SOUND–MUSIC-MIDI-SPEECH Mr.Bimal Kumar Ray Dept. of Information Science & Telecommunication Ravenshaw University Fundamentals of Multimedia Dept of IST, Ravenshaw University

2. What is Sound/Audio • The perception of sound by human beings is a very complex process. • The detector which receives and interprets the sound. • Sound is the combination of both high and low pressure which is propagated through the air medium in the form of wave. • Sound is a physical phenomenon(situation) produced by the vibration of matter and transmitted as waves. • Sound is always Non-periodic. • Sound is mechanical wave that is an oscillation of pressure transmitted through a solid,liguid,gas composed of frequency within the range of hearing. • To create sound your computer feeds electricity at a certain wave length through speaker. • Every sound is compression of waves of many different frequencies and shapes. But the simplest sound we can hear is a sine wave. Fundamentals of Multimedia Dept of IST, Ravenshaw University

3. What is Sound/Audio • Sound waves can be characterised by the following attributes: Period, Pitch, Volume, Frequency, Amplitude, Bandwidth, sampling, Loudness and Dynamic. • Period: the interval at which a periodic signal repeats regularly. • Pitch: a perception of sound by human beings. It measures how ‘high’ is the sound as it is perceived by a listener. • Volume: the height of each peak in the sound wave • Frequency:(sometimes referred to as pitch) the distance between the peaks. The greater the distance, the lower the sound. Fundamentals of Multimedia Dept of IST, Ravenshaw University

4. What is Sound/Audio • Loudness: important perceptual quality is loudness or volume. • Amplitude: is the measure of sound levels. For a digital sound, amplitude is the sample value. • The reason that sounds have different loudness is that they carry different amount of power. the unit of power is watt. • The sounds is measured the unit Bel or more commonly deciBel (dB). examples for • 160 dB Jet engine • 130 dB Large orchestra • 100 dB Car/bus on highway • 70 dB Voice conversation • 50 dB Quiet residential areas • 30 dB Very soft whisper • 20 dB Sound studio Fundamentals of Multimedia Dept of IST, Ravenshaw University

5. What is Sound/Audio • To include sound in a multimedia application, the sound waves must be converted from analog to digital form • This conversion is called sampling every fraction of a second a sample the of sound is recorded in digital bits Two factors affect the quality of digitized sound • Sample rate – the number of times the sample is taken • Most common sampling rates are: 11.025, 22.05, and 44.1 kHz • Sample size – the amount of information stored about the sample • Most common sampling sizes are: 8 and 16 bit Fundamentals of Multimedia Dept of IST, Ravenshaw University

6. What is Sound/Audio • Dynamic: range means the change in sound levels. • For example, a large orchestra can reach 130dB at its climax and drop to as low as 30dB at its softest, giving a range of 100dB. • Bandwidth: is the range of frequencies a device can produce, or a human can hear FM radio: 50Hz – 15kHz Children’s ears: 20Hz – 20kHz Older ears: 50Hz – 10kHz Ultra-sound 20kHz – 1GHz Hyper-sound 1GHz - 10THz Fundamentals of Multimedia Dept of IST, Ravenshaw University

7. Computer Representation of Sound • Sound waves are continuous while computers are good at handling discrete numbers. • In order to store a sound wave in a computer, samples of the wave are taken. • Each sample is represented by a number, the ‘code’. • This process is known as digitisation. • This method of digitising sound is know as pulse code modulation (PCM) • This is why one of the most popular sampling rate for high quality sound is 4410Hz. • Another aspect we need to consider is the resolution, i.e., the number of bits used to represent a sample. • 16 bits are used for each sample in high quality sound • Different sound card have different capability of processing digital sounds. Fundamentals of Multimedia Dept of IST, Ravenshaw University

8. Computer Representation of Sound Recording and Digitising sound: • An analogue-to-digital converter (ADC) converts the analogue sound signal into digital samples. • A digital signal processor (DSP) processes the sample, e.g. filtering, modulation, compression, and so on. Play back sound: • A digital signal processor processes the sample, e.g. decompression, demodulation, and so on. • A digital-to-analogue converter (DAC) converts the digital samples into sound signal. Fundamentals of Multimedia Dept of IST, Ravenshaw University

9. Quality vs File Size • The size of a digital recording depends on the sampling rate, resolution and number of channels. • S = R x (b/8) x C x D • Higher sampling rate, higher resolution gives higher quality but bigger file size. S file size bytes R sampling rate samples per second b resolution bits C channels 1 - mono, 2 - stereo D recording duration seconds Fundamentals of Multimedia Dept of IST, Ravenshaw University

10. Quality vs File Size • For example, if we record 10 seconds of stereo music at 44.1kHz, 16 bits, the size will be: • S = 44100 x (16/8) x 2 x 10 = 1,764,000bytes = 1722.7Kbytes = 1.68Mbytes Note: 1Kbytes = 1024bytes 1Mbytes = 1024Kbytes • High quality sound files are very big, however, the file size can be reduced by compression. Fundamentals of Multimedia Dept of IST, Ravenshaw University

11. Audio File Formats The most commonly used digital sound format in Windows systems is .wav files. • Sound is stored in .wav as digital samples known as Pulse Code Modulation • Each .wav file has a header containing information of the file. • type of format, e.g., PCM or other modulations • size of the data • number of channels • samples per second • bytes per sample • There is usually no compression in .wav files. • Other format may use different compression technique to reduce file size. • .vox use Adaptive Delta Pulse Code Modulation (ADPCM). • .mp3 MPEG-1 layer 3 audio. • RealAudio file is a proprietary format. (.ra .ram .rm) Fundamentals of Multimedia Dept of IST, Ravenshaw University

12. Audio File Formats • WMA: Windows Media Audio (.wma) Windows Media Audio is a Microsoft file format for encoding digital audio files similar to MP3 though can compress files at a higher rate than MP3. • MOV (movie):basically a video format where the pictures are omitted. • RIFF:Resource Interchange File Format a Microsoft developed format capable of handling digital audio and MIDI. • SDMI: (Secure Digital Music Interface) Designed to protect against most forms of unauthorised copying • SND (sound): limited to 8 bits with interpreters for the PC available. • Ogg (.ogg): Ogg is an audio compression format, comparable to other formats used to store and play digital music. It uses a specific audio compression scheme that's designed to be contained in Ogg. Fundamentals of Multimedia Dept of IST, Ravenshaw University

13. Audio File Formats • AIFF: Audio Interchange File Format is mostly used by Silicon Graphics. AIFF files are easily converted to other file formats, but can be quite large. One minute of 16-bit stereo audio sampled at 44.1 kHz usually takes up about 10 megabytes. • Dolby Digital Surround Sound: Also known as AC3 (Audio Coding), or Dolby 5.1 (where .1 indicates subwoofer bass channel). Dolby Digital has been chosen as the standard sound technology for DVD (digital video disk) and HDTV (High definition TV). • Dolby Digital Surround Sound Digital Track on Film: It is a digital encoded system of 6 separate and independent surround sound channels, for 6 speakers (Front (Left/right), Rear (left/right), Front center and Sub-woofer. • MIDI - Musical Instrument Digital Interface (.mid) MIDI representation of a sound includes values for the note‘s, pitch, length, and volume. It can also include additional characteristics, such as attack and delay time. Fundamentals of Multimedia Dept of IST, Ravenshaw University

14. MUSIC • Music can be described in a symbolic way. • Music is the art of arranging tones in an orderly sequence so that produce a sound.  • Music is an art form whose medium is sound and silence. • Music common elements are pitch, notes, scales and tempo etc. • Any sound may be represent in that way including music. Fundamentals of Multimedia Dept of IST, Ravenshaw University

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