Activity 1 - Digitising Sound For the following text insert the words underneath into the blank spaces. Q1. For the following text insert the words underneath into the blank spaces. digital signal microphone analogue analogue-to-digital converter Sound is an ____________ sound wave. To save this on a computer a ____________ converts it to an electrical analogue signal. An ____________ converts it to a ____________ which the computer can then save. [4] Q2. The quality of sound saved in an audio file is determined by both the bit rate and what? Q3. If the bit rate of a sound file is increased what happens to the audio quality? Highlight one box The bit rate has no effect It increases It decreases Challenge: Activity 2 - Impact of Bitrate and Sample Rate Answer the questions below about sound. 1. Explain how an increase in bitrate can increase the quality of a sound file. [3] 2. What is meant by the term ‘sample rate’ and what affect would an increase in sample rate have on a sound file? [3] Activity 3 - Calculating File Sizes Use the formula below to answer the To calculate the number of bits required to store a sound file you would need to do this: file size = (bit rate x sample rate x (minutes x 60)) E.g. A 4-bit sound file with a frequency of 100hz that is 2 minutes long would be calculated like this: 4 x 100 x (2 x 60) 48 000 bits or 6 000 bytes or 6 kilobytes Question: An audio CD has a bit-rate of 16 bits. It has a frequency (sample rate) of 44,100 Hz for each of the left and right speakers How many bits are required to store 1 second of audio for both speakers? How many bytes are required to store 1 minute of audio? A 650 MB CD can store how many minutes of audio?
Answers
Answer:
A-Type Plug — A domestic and semi-pro form of jack plug, also known as TS or TRS and widely used for electric instruments, headphones and line-level connections on semi-pro equipment. (cf. B-Type Plug)
A-Weighting — A form of electrical filter which is designed to mimic the relative sensitivity of the human ear to different frequencies at low sound pressure levels (notionally 40 Phons or about 30dBA SPL). Essentially, the filter rolls-off the low frequencies below about 700Hz and the highs above about 10kHz. This filtering is often used when making measurements of low-level sounds, like the noise floor of a device. (See also C-Weighting and K-Weighting)
AC — Alternating Current (cf. DC). Audio signals are represented in the electrical domain as currents flowing alternately forward and back in the circuits as an analogue of the compression and rarefaction of acoustic air pressure.
Accent Mic — see Close Miking
Acoustic Foam — A specific type of open-celled expanded polyurethane foam that allows sound waves to enter and flow through the foam, absorbing their energy and preventing them being reflected. The density and depth of the foam affects the frequency range over which it is effective as an absorber.
Acoustic Treatment — A generic term embracing a range of products or constructions intended to absorb, diffuse or reflect sound waves in a controlled manner, with the intention of bestowing a room with an acceptable reverberation time and overall sound character.
Active — Describes a circuit containing transistors, ICs, tubes and other devices that require power to operate, and which are capable of amplification.
Active Loudspeaker or Monitor — A loudspeaker system in which the input signal is passed to a line-level crossover, the suitably filtered outputs of which feed two (or more) power amplifiers, each connected directly to its own drive unit. The line-level crossover and amplifiers are usually (but not always) built in to the loudspeaker cabinet.
A/D [A-D] Converter — A device which converts an analogue audio signal into a digital representation.