Sound representation - 92 - 95 Flashcards
What is analogue signal?
Natural sound waves, occurring in continuous wave form, for example, human voice
What is digital signal?
Discrete digital format for representing natural soundwaves
eg CDS AND DVDS, Binary data
What are ADCs?
An analog to digital converter is any device, which can convert continuous natural soundwaves into a digital format
What are ADCs used for? and how do they work
(ADCs) are used to convert analog signals (continuous signals) into digital data that computers and digital devices can process
- used in medical equipment
- amplitude of signal is measured
- measurement coded in binary
What is a DAC
A digital to analog converter is any device, which can convert a digital audio signal into a continuous natural soundwave
What affects the quality of the digitally converted soundwave?
The sampling rate and the sampling resolution
What is the sampling rate in simple terms?
The speed
What is the sampling resolution in simple terms?
The detail
What is sampling rate?
- the frequency at which you record the amplitude of a sound wave
- The more often you record a sample the smoother the playback will sound
What is sampling rate measured in?
Hertz
Advantages and disadvantages of increasing the sample rate
Advantage: the sample will be smoother and more detailed.
Disadvantage: the file will take up more space, as more information will need to be stored
what does the sampling resolution reprpesent
It represents how many different gradations of amplitude can be represented in a digital waveform
- bits per sample
What is sample resolution measured in?
Bits
Advantages of increasing the sample resolution
It’s a more accurate representation of the wave and will sound better
What does Nyquist theorom state
to produce an accurate recording, you need to use a sampling rate, which is at least double that of the highest frequency in the original signal
What frequency can human ears hear?
20 Hz to 20,000 Hz
proof of nyquist theorom
Humans can hear from 20 Hz to 20,000 Hz and modern digital audio samples at around 44,100 Hz
How to calculate the size of the sample?
= Number of samples per second X Number of bits per sample X Length of sample in seconds
What is MIDI?
It is a technical standard, which describes:
A protocol, a digital interface or a standard set of connectors
Why is MIDI used
It allows for a wide range of electronic musical instruments or computers to communicate with each other
How does MIDI work?
- music represented as sequence of MIDI events messages
- example of data contained in a message may be pitch, volume, velocity
What do events messages specify?
Duration of note
Pitch
Volume change
Velocity
Vibrato
Tempo synchronisation
Summarise, MIDI
- they are a list of instructions
- which detail how to synthesise a sound
- these sounds being pre recorded digital samples of real instruments
Advantages of MIDI
- more compact representation
- it makes it easier to modify notes
- simple method to compose algorithmically
- no data lost about musical notes
- musical score can be generated directly from a MIDI file
how to convert analogue to discrete
measure and record the amplitude of a sound wave at given time intervals. the more frequently the samples are taken, the more accurately the sound will be represented
how to increase the accuracy of a sound sample
increase audio bit depth
process of analogue to digital (step by step)
- ADC takes samples of the signal at regular intervals
- the samples are quantised
- each sample is coded into a binary value
what is frequency determined by
the speed of oscillation/vibration of a wave
what is the sample resolution
the number of bits per sample
how long are MIDI messages
- usually 2 to 3 bytes long
- first byte is a status byte
how does DAC work
A DAC converts a digital signal into a continuous analogue signal by interpolating the discrete values and smoothing the result
