Ed's AV Handbook.com
Home Theater & High Fidelity Stereo Audio


Chapter Three
Sound Reproduction
Page 3

Batting practice for the audio/video pro and a primer for the novice
 


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The 21st Digital Century

          Audio playback once seeemed as simple as placing a record on a turntable and engaging the play button.  But 20th Century memories can be short.  It really wasn't always that simple.  For example, the playback of an LP record could include several sizes in one of four speeds.  Plus prior to 1954 LP vinyl enthusiast were confronted with several playback equalization choices.  In addition, tape formats such as the open reel or cassette included options such as tape size, speed, noise reduction, playback equalization, and record bias. Given this history, it shouldn't be surprising that the 21st digital century has also generated yet another collection of options wrapped in terms such as file and format, compressed or uncompressed, lossless or lossy, WMA, ACC, MQA.  

Files & Formats
          Digital audio is organized into files and formats.  The file is the container.  The format
is the storing method.  The compact disc files audio to an optical disc and uses the
Sony/Phillips 16bit 44.1KHz sampling rate format.  
          Audio can also be filed to a music server hard drive, flash drive, solid state drive, or streamed from an Internet cloud server.   This type of audio file management must choose between a compressed or uncompressed format.
Uncompressed Format
          An uncompressed format records the entire audio wave form.  
This format can devour limited computer storage and Internet bandwidth.  On the plus side computer storage prices are falling.  In addition an uncompressed digital recording can outperform the CD.  Hard drive or solid state drive playback eliminates phase (jitter) distortion created by the laser read optical disc.  Uncompressed formats include FLAC uncompressed, WAV, AIFF, MQA, plus the DSD DFF & DSF formats.
 

Handbook Note: codec is shorthand for encode/decode

Compressed Format
          A compressed format saves computer storage and Internet bandwidth as it shrinks data files
by removing 'uneeded' data with masking codec software.  Masking records louder lower frequency audio as less loud higher frequencies of the same phase are removed.  This missing audio data is said to go unoticed because its loss is hidden or masked by the louder audio.  There are two versions of compressed formats --  lossless and lossy.

Lossless
          Lossless compression reduces data and data space by 50%.  Surprisingly lossless can compete with CD quality audio.  Apparently it's a toss up between the 'lost redundant' data and optical laser jitter.  Common lossless formats include ALAC, and FLAC lossless (which is not supported by Apple's iTunes).

Lossy
          Lossy reduces data and data space by 90%.  It does not approach CD quality sound. Lossy sound quality ranges from a cell phone to good FM radio.  MP3, OGG Vorbis, and ACC iTunes are popular lossy formats.

Masking Comment
          Masking implies that the lost redundant audio is insignificant.  However that missing data includes essential phase information.  Sound engineers have proven that the human ear is more sensitive to phase than frequency.  As a friend once explained; it was more important for early caveman to determine which direction (phase) a tiger was coming from than which tiger (frequency).  We are descendants of the former.  
          Phase distortion is a well know issue in high fidelity circles.  
Phase distortion has long been identified as a key hindrance of the compact disc.  Masking creates phase distortion.
          For further insight --
check out the MQA story, 'Muscial Origami', at my 'Ed's AV Blog' page.  Bob Stuart of Meridian Audio has introduced a recording format that eliminates phase distortion - "Master Quality Authenticated' audio codec".

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Ed's AV Handbook.com
Batting Practice for the AV Pro and a Primer for the Novice.
Copyright 2007 Txu1-598-288   Revised 2018