CGMA UNIT 6 part 2
Digital audio is music, speech, and other
sounds represented in binary format for use in
digital devices. Most digital devices have a built-in
microphone and audio software, so recording
external sounds is easy.
To digitally record sound, samples of a sound
wave are collected at periodic intervals and
stored as numeric data in an audio file. Sound waves are sampled many times per
second by an analog-to-digital converter. A digital-to-analog converter transforms the
digital bits into analog sound waves.
The most popular digital audio formats are: AAC, MP3, Ogg, Vorbis, WAV, FLAC, and WMA.
Some Characteristics of Sound
Digital Representation of Audio is needed. It must convert wave form to digital using:
1. Sample: It is a process of measuring amplitude at equally-spaced moments in time, where each measurement constitutes a sample. The number of samples taken per second(samples/s) is the sampling rate. Units of samples are also referred to as Hertz(Hz).
2. Quantization: It is a process of representing the amplitude of individual samples as integers expressed in binary. The fact that integers are used forces the samples to be measured in a finite number of discrete levels. The range of the integers possible is determined by the bit depth, the number of bits used per sample. A sample's amplitude must be rounded to the nearest to the allowable discrete levels, which introduces error in the digitaization process.
Recording Digital Audio
Digital audio is an audio signal encoded in a digital form. It is more reliable than analogue ausio, which is susceptible to noise and distortion. It is a method of preserving sound in which audio signals are transformed into a series of pulses that correspond to patterns of binary digits (i.e. 0's and 1's) and are recorded as such on the surface of a magnetic tape or optical disc. A digital system samples a sound's wave form, or value, several thousand times a second and assigns numerical values in the form of binary digits to its amplitute at any given instant. A typical digital recording system is equipped with an alalog-to-digital converter that transforms two channels of continuous audio signals into digital information, which is then recorded by a high- speed tape or disc machine. The system uses a ditital-to-analog converter that reads the encoded information from the recording medium and changes it back into audio signals that can be used by the amplifier of a conventional stereo sound system.
Audio standards for Multimedia Applications
The most popular digital audio formats are: AAC, MP3, Ogg, Vorbis, WAV, FLAC, and WMA.
Some Characteristics of Sound
- Amplitude
- Wavelength (w)
- Frequency (Y )
1. Sample: It is a process of measuring amplitude at equally-spaced moments in time, where each measurement constitutes a sample. The number of samples taken per second(samples/s) is the sampling rate. Units of samples are also referred to as Hertz(Hz).
2. Quantization: It is a process of representing the amplitude of individual samples as integers expressed in binary. The fact that integers are used forces the samples to be measured in a finite number of discrete levels. The range of the integers possible is determined by the bit depth, the number of bits used per sample. A sample's amplitude must be rounded to the nearest to the allowable discrete levels, which introduces error in the digitaization process.
Recording Digital Audio
Digital audio is an audio signal encoded in a digital form. It is more reliable than analogue ausio, which is susceptible to noise and distortion. It is a method of preserving sound in which audio signals are transformed into a series of pulses that correspond to patterns of binary digits (i.e. 0's and 1's) and are recorded as such on the surface of a magnetic tape or optical disc. A digital system samples a sound's wave form, or value, several thousand times a second and assigns numerical values in the form of binary digits to its amplitute at any given instant. A typical digital recording system is equipped with an alalog-to-digital converter that transforms two channels of continuous audio signals into digital information, which is then recorded by a high- speed tape or disc machine. The system uses a ditital-to-analog converter that reads the encoded information from the recording medium and changes it back into audio signals that can be used by the amplifier of a conventional stereo sound system.
Audio standards for Multimedia Applications
Audio standards are different file foramts avilable in multimedia applications. Some of these file formats are:
1. WAV:- WAV files are uncompressed audio, also known as lossless audio files. This preserves all the original characteristics of the digital audio signal. A WAV file comprises a header and then all the individual samples. WAV files are recognized by all quality audio editing software. They are most commonly used when working on a windows PC.
2. AIFF (or AIF):- The Audio Interchange Format File is the Mac OS equivalent of WAV files. They are of equivalent standard, and are the audio format of choice for audio engineers working on a Mac. However, you can almost always use AIFF and WAV on both Mac and Windows PC.
3. MP3:-MP3s are digital audio files that are encoded using lossy compression format. When a WAV or AIF file is compressed to MP3, those parts of the recoreded audio that the human ear has difficulty hearing, or that make little difference to the overall sound of the original are discarded in the compression precoss.
The great advantage of the MP3 format is its drastically reduced file size. This makes it suitable for easy distribution over the internet, and allow small devices such as iPods to store many more files than would otherwise be possible.
4. WMA:- Windows Media Auiod is another lossy compression format, which was developed by Microsoft. It was introduced as a competitor to the MP3 file, though has never been widely used.
5. OGG:- The OGG vorbis format is an audio codec (encoder/decoder) that is open sourse and free. It uses lossless compression and is generally considered to deliver a superior audio quality to MP3. However, files rendered in this format cannot always be played on the most popular portable audio devices.
6. MID:-MIDI data is often stored in MIDI files(MID). MIDI data and audio recordings are not the same thing so MIDI files are comparatively very small. This is because they do not contain any information about how tracks sound. They only contain control information to determine how MIDI instruments should be played.
The most coomon audio file formats are WAV, AIF and MP3.
1. WAV:- WAV files are uncompressed audio, also known as lossless audio files. This preserves all the original characteristics of the digital audio signal. A WAV file comprises a header and then all the individual samples. WAV files are recognized by all quality audio editing software. They are most commonly used when working on a windows PC.
2. AIFF (or AIF):- The Audio Interchange Format File is the Mac OS equivalent of WAV files. They are of equivalent standard, and are the audio format of choice for audio engineers working on a Mac. However, you can almost always use AIFF and WAV on both Mac and Windows PC.
3. MP3:-MP3s are digital audio files that are encoded using lossy compression format. When a WAV or AIF file is compressed to MP3, those parts of the recoreded audio that the human ear has difficulty hearing, or that make little difference to the overall sound of the original are discarded in the compression precoss.
The great advantage of the MP3 format is its drastically reduced file size. This makes it suitable for easy distribution over the internet, and allow small devices such as iPods to store many more files than would otherwise be possible.
4. WMA:- Windows Media Auiod is another lossy compression format, which was developed by Microsoft. It was introduced as a competitor to the MP3 file, though has never been widely used.
5. OGG:- The OGG vorbis format is an audio codec (encoder/decoder) that is open sourse and free. It uses lossless compression and is generally considered to deliver a superior audio quality to MP3. However, files rendered in this format cannot always be played on the most popular portable audio devices.
6. MID:-MIDI data is often stored in MIDI files(MID). MIDI data and audio recordings are not the same thing so MIDI files are comparatively very small. This is because they do not contain any information about how tracks sound. They only contain control information to determine how MIDI instruments should be played.
The most coomon audio file formats are WAV, AIF and MP3.
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