Digital Recording Flashcards
Digital
Quantizing = dynamic range
sampling rate = frequency response
Sampling
Incoming analog signal is captured at periodic intervals
a digital snap shot of the sound is taken
Nyquist theorem
Sampling frequency (rate at which samples are taken )must be at least two times higher than highest audible frequency to be reproduced one sample for each phase of a waves cycle
Sampling 2
Frequencies about the range of human hearing can be ALiased or converted into audible noise and therefore must be filtered out before sampling
Anti aliasing
Involves a low pass filter nearly of a brick wall type which abruptly reduces the volume of frequencies above a certain point
Distribution standards CD - 44.1 kHz /DVD video -48kHz
Highest currently supported - 192 kHz (production) 96 kHz (blu ray)
Quantizing
Sometimes referred to as resolution technique of incrementing a continuous analog event into a discrete set of bits for storage or manipulation the more bit levels the wider the dynamic range 6 dB per bit
Dist. Standard cd 16 bit DVDs video 24 bit
Highest supported - 24 bit blu Ray
Quantizing continued
Incoming audio is broken down into a series of discrete voltage steps
Each step is coded into a binary
word that digitally represents the signal level with as much accuracy as the word length allows
The process
1 anti-aliasing –Unwanted highs filtered out
2 sample – and –hold– Signal held and examined for duration of one sampling cycle
3 A to D conversion – DC voltage translated into binary word
4 Data coding – words grouped into block for recognition with an bitstream
- like putting a space between words so that we can read them more easily
5 error correction – use of interleaved check code to check the accuracy of each binary word to guard against degradation
6 Data modulation – bits changed into appropriate form for recording medium
Eg magnetic pulse/ no pulse for tape PCM or laser fires to burn dark pit/no dark pit for optical Cd
Digital audio recording media two categories
Drives
A magnetic – physically works the same way as magnetic tape example hard drives
B optical – use a burning or scanning laser to write or read data respectively example CD and DVD
C Flash memory – store electrons on a grid each representing a binary zero or one
2 magnetic tape
A stationary head (look like open reel analog recorder) *Most often used for large-format tracks 32/48 tk
B Rotary head – most often used for ST small format multitrack 8–24 tracks and modular digital multi tracks A-DAT/DA-88
Determining file size
Sampling rate x duration in seconds x resolution/8 x number of tracks then convert GB/MB ( divide 1,024)
File types and file compression for transmission
Uncompressed files linear PCM WAV .wav AIFF .aif Broadcast WAV .wav Sound designer II .sd2 Lossless compression formats windows media . Wma Apple lossless .m4a FLAC .flac Lossy compression formats MPEG audio - .mpa mp2 MP3 MP4 Advanced audio coding AAC .m4a Ogg vorbis .ogg Cross-platform formats (allows multitrack files exchange across DAWS AND OSs) AES-31 OMF
Analog
Speed equals dynamic range
width equals frequency response
