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Sound - Coggle Diagram
Sound
Sound metadata
In order for an audio player to play back a sound file, the file itself needs to contain some additional basic information as well as the samples. This extra information is called 'metadata' and it is usually embedded at the beginning of the file.
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The Codec is a shortening of Code Encode and describes the algorithm used to create and play back the file. In this case the codec is the MPEG 1 Layer III algorithm.
File formats such as MP3 support a large number of extra metadata. For mp3 the metadata are also called 'tags'. Here is a short list of common tags:
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advantages of sampling
It is more portable; it can be carried on a memory stick or SD card while a vinyl record or tape are not as possible
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Digital audio files can be easily emailed, downloaded and streamed by users
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Sample / frequency rate
the sample rate is how many samples, or measurements, of the sound’s amplitude are taken each second.
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the more samples that are taken, the more detail about the waves so the higher the quality of the audio.
also, the shape of the sound wave is captured more accurately.
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Bit depth
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the higher the bit depth, the higher the quality of the audio.
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bit depth of 16 has 65,536 possible values (216).
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old computer games had a bit depth of 8 which is just 256 possible values (28) - very poor quality compared to today’s standards!
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Channels
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mono sound
has information about only a single source, or "channel"
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surround sound
has multiple channels, to make use of multiple speakers
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Bit rate
the bit rate of a file tells us how many bits of data are processed every second. bit rates are usually measured in kilobits per second (kbps).
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a typical, uncompressed high-quality audio file has a sample rate of 44,100 samples per second, a bit depth (the number of bits available for each sample) of 16 bits per sample and 2 channels of stereo audio. the bit rate for this file would be:
44,100 samples per second × 16 bits per sample × 2 channels = 1,411,200 bits per second (or 1,411.2 kbps)
sound card
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A sound card has two jobs. It has to be able to convert an analogue signal into a digital one for storage. It also has to be able to convert stored digital signals into an electrical signal to send to the speakers.
The first job is performed by the Analogue-to-Digital Converter (ADC). The second is performed by the Digital-to-Analogue Converter (DAC). We will discuss how this happens in later pages.
Frequency
The higher the frequency, the higher the pitch of the sound
As you get older, you stop being able to hear really high pitch sounds
The speed at which molecules vibrate is called frequency. This is measured in Hertz (vibrations or cycles per second)
dynamic range
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if there is a low dynamic range, loud sounds become distorted and quiet sounds are inaudible.
the maximum signal-to-noise ratio. to use sound as the example, this is the ratio of the loudest (undistorted) signal to that of the quietest (discernible) signal in a system as expressed in decibels (db).
file size
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This will give you an answer in bits (though it's usually convenient to convert this further to bytes).
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Sound
Sound is caused by molecules vibrating (e.g. air, water, metal)
Sound is represented using wave graphs: x axis= time in seconds, y axis = change in pressure (caused by vibration)
sampling
Sampling is a method of converting an analogue sound signal into a set of binary numbers that are then stored in a digital file.
It involves taking a physical measurement of the amplitude of a sound wave at set time intervals - usually several thousand times per second
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Microphone
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A microphone is an input device for sensing incoming sound. It converts sound into an electrical signal. This signal is then passed on to the ADC (Analogue-to-Digital converter) in the sound card.
speaker
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To replay a sound, the file is opened and the binary numbers are fed through the DAC (digital-to-analogue converter) which is then amplified in some way (internal or external amplifier) to produce enough power for the speakers or ear-phones you are using.
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cd sample frequency
common audio sample rate for music is 44,100 samples per second (cds) – the unit this is measured in is hertz – this is 44,100 hertz or 44.1 kilohertz (khz)
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voip sample frequency
telephone networks and voip (voice over internet protocol) services (e.g. skype) use a sample rate as low as 8 khz