P2 T1 L11 - Representing sound Flashcards
(Real world data)
Real-world data is usually ________ in nature with values that vary by any amount over time
Sound is a result of changes in air pressure.
Pressure fluctuations cause our eardrums to vibrate.
Nerve signals are interpreted as sound.
analogue
(Analogue and digital signals)
Analogue signals are _________, whereas digital signals are _______.
Signals can be converted from one form to another.
continuous
discrete
(Analogue to digital convertors)
Give 1 example of ADCs and 1 example of DACs
NOTE:
ADC - Analogue to Digital Convertor
DAC - Digital to Analogue Convertor
ADC: Microphones
DAC: Speakers
Explain analogue to digital conversion
3 steps
- Analogue sound samples are recorded via an amplifier.
- Each sample is quantised to measure its wave height and translate this into an integer value.
- The integer value is then converted and stored digitally as a binary value.
(Sampling)
An analogue signal is measured at regular _______.
The _________ (or voltage of the analogue signal at that point in time).
The number of ______ ____ __ ____ ______ (referred to as the sampling rate and is measured in Hertz).
periods
amplitude
amples taken in one second
(Sample resolution)
The number of bits (audio bit depth) used to record each measurement is known as the ________.
More bits used per sample enables the height of the wave to be more accurately measured but increases ____ ____.
resolution
file size
(Sampling rate)
The total number of waves produced in one secondis called the ________.
The ________ or sample rate per second affects the level of detail in the digital representation.
The greater the ________, the greater the accuracy, and file size.
frequency
frequency
frequency
(File size)
The sampling rate and the resolution allow us to determine the size of file required to create a digital copy of the sound waves.
________ ____ indicates number of samples per second (Hertz)
________ is number of bits used per sample.
File size = _______ ____ * _________ * _______ __ _______
Sampling rate
Resolution
sample rate * resolution * length in seconds
(Real sound)
Sound in the real-world is made up of combinations of different __________.
A sound wave is a combination of these different __________.
frequencies
frequencies
(Sampling limitations)
There is a limit on the lowest sampling rate (fs) that can be used for an accurate recording
Because sound is made up of many components each at different frequencies, samples must be ______ the highest frequency in order to replicate the original sound wave. (In practice, this means that your sample will catch the variations between the sound waves).
This concept is known as the Nyquist Theorem: fs > 2fmax
twice
(MIDI)
The MIDI (which stands for: ________ _______ _______ ______) standard creates sounds as requested either from an instrument of piece of software
It is not a live recording but a synthesised sound.
Musical Instrument Digital Interface
(MIDI benefits)
With this system the full sound signal does not need to be transmitted, only the _________ to play the sound.
It is up to the _________ to create the sound.
This significantly reduces the amount of _____ _________.
As sounds are _________, they may be less realistic.
instructions
instrument
data transferred
synthesised
(Event messages)
A MIDI sound processor can be linked to several instruments or computers
This can send a timed sequence of event messages to: (to do 4 things)
- Synchronise tempo
- Control pitch
- Change volume
- Introduce and silence other instruments in a digital orchestra
(The human ear)
Humans can hear frequencies of between __Hz and __kHz
This reduces as we ____.
20 22
age
(Plenary)
Real world analogue sound data can be ________
Sound is sampled at a specified ____ and ________.
Signals can change due to ___________ but this can be detected
MIDI is an alternative system for producing ______.
digitised
rate and resolution
interference
sound
