| Describe how bit patterns may be used to represent sound | As the amplitude of the sound being represented by a binary number
Amplitude is taken at given time intervals
Think of a graph |
| Whats Nyquist theorem | Sampling rate of a digital audio file = 2 X frequency
For the sound for the audio to be accurate |
| Define MIDI | It’s a protocol for transferring digital instrumentional data |
| Whats the difference between analogue and digital | Analog signal is represented by the sine waves when the digital signal is represented by square waves
Analogue data is continuous, there are no limits to the values that the data can take. In contrast, digital data is discrete, meaning that it can only take particular values |
| Describe the principles of operation of an ADC | An ADC is used
The device works by taking a reading of an analogue signal, through an analogue sensor, at regular intervals and recording the value in a process called sampling
Samples are taken at a specific frequency which determines the number of samples taken per second
This can then be stored digitally as a bit pattern |
| How do you calculate the size of a sound sample | sampling rate X sample resolutuion X duration = size in bits |
| Describe the principles of operation of a DAC | A DAC is used
The device reads a bit pattern representing an analogue signal and outputs an alternating, analogue, electrical current |
| Whats the most common use for a DAC | convert a digital audio signal to an analogue signal
So speakers |
| What are ADCs used in conjuction with? | Analogue sensors |
| Whats are event messages in MIDI | MIDIs storage of sound
Each of which indenpedently represents a different musical event |
| Give some examples of event messages in MIDI | ● The duration of a note
● The instrument with which a note is played
● How loud a note is (its volume)
● If a note should be sustained |
| Whats the advatages of using MIDI over a sampled recording of a piece of music | Easy manipulation of music without loss of quality
MIDI files are often smaller in size than sampled audio files and are lossless so there’s no information lost when music is stored using MIDI. |
| Whats the disadvatages of using MIDI over a sampled recording of a piece of music | MIDI can't be used for storing speech
Sometimes results in a less realistic sound than sampled recordings |
| Define sample rate | Number of samples per second |
| How is sound represented by computers? | As a sequence of samples
Or series of messages (MIDI) |
| What are the pros and cons to increasing the sampling resoltion | Better quality but greater file size |
| State what sample resolution is | Number of bits allocated to each sample |
| Explain the differences between the way in which sound is recorded for MIDI and ADC/DAC | Storage of sound as a series of event messages rather than samples |
