Chapter 2 - Digital Audio Flashcards
What is sampling?
The process of measuring a waveform as it passes by at a set rate per secend.
What is quantization?
Measuring the amplitude of each sample and assigning a binary word to it. The binary word expresses the amplitude of each sample.
Decimal system is base 10. Binary is base ___.
2
What is CD quality sample rate?
44.1KHz
State the Nyquist theorem.
In order to accurately encode audio, your sampling frequency must be at least double the highest frequency you want to record.
What is alias filtering?
An extremely steep low pass filter that removes all frequencies above half of the sampling frequency.
What is Quantising error?
When a sample falls between two quantisation steps and is rounded up or down.
What do Quantisation errors sound like?
Noise
How do you reduce Quantising errors?
Increase the bit rate
What is Dither?
Dither is a small amount of white noise equal to one quantising level.
What is dither used for?
It smooths out the stepped transfer plat that results from the digitizing process.
What are the last two steps in a digital recording chain, after A/D converter?
Multiplexing and error correction.
What does a multiplexer do?
Converts the parallel binary bit words to serial data.
Name the 3 types of error detection/ correction.
- Even Parity Check
- Interleaving
- Concealment/ Interpolation
How does Even Parity Check work?
An extra bit is added to the original data so that the total number of 1’s in each word is an even number. If one bit becomes corrupt the parity check will fail and the data will be flagged as invalid.
What does CRCC stand for?
Cyclic Redundancy Check Code
how does CRCC work?
A binary word representing the number of ones in the sample is generated and added to the end of the sample. Any disagreement between the received checksum and that formed from the received data would indicate with high probability that an error has occurred.
How does interleaving work?
the data is scattered around the medium in a known sequence. Any damage to the data is minimized when the data is reordered into the correct linear order.
How does Concealment/ Interpolation work?
Last resort. If the data of a sample become corrupt, the missing data can be regenerated by looking at the amplitude of the previous and following sample and working out the average between the two.
Name the uncompressed MAC audio file.
AIFF
Name the compressed version of AIFF.
AIFC
