Section 3 Chapter 17 - Digital Representations of Sound Flashcards
Audio bit depth (Sample resolution)
The number of bits used to store the sound waves amplitude
Sampling rate
The frequency at which the amplitude is recorded
Equation for the size of an audio file
sample rate * bit depth * length (* 2 if stereo)
Process of converting analogue sound to digital sound
Sounds –> Amplifier –> ADC
Process of converting digital sound to analogue
Digital sound –> DAC –> Amplifier –> Speaker
Frequency of a wave
The speed of oscillation
Nyquist’s theorem
In order to produce an accurate recording the sampling rate must be at least double the frequency of the highest frequency in the recording
Sampling rate of a CD
44,100 Hz
MIDI file
A type of music file which synthesises sounds based on pre-recorded digital samples and synthesised samples
Advantages of a MIDI file (2)
- Uses far less disk space
- Easily manipulated as the instrument or key can be easily changed
Advantage of conventional waveform sound files
Can be used to store actual recordings of sound and voices
MIDI event messages
MIDI files can be used to send event messages to electronic instruments or computers to:
- Synchronise tempo
- Control pitch
- Control volume
Examples of MIDI metadata (5)
- Duration of the note
- Instrument
- Volume
- Timbre
- Channel
Difference between analogue and digital data
Analogue has a theoretically infinite precision as it is based in the real world. Digital precision is limited to the number of bits used to store it.
Difference between analogue and digital signals
Analogue signals can have any amplitude whereas digital signals can only have fixed amplitudes (i.e. the precision is lower)
