iTunes and Music File Formats

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iTunes and Music File Formats Carl
Ebhardt T-MUG June12, 2006
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Introduction Frequency range of voice and
music A above middle C is 440 Hz Each octave
doubles or halves the frequency Basic Theory
Behind Digitizing Analog Sound Sampling rate
gt2X the highest frequency Encoding bits per
sample 8 bits (256) is plus/minus 2
error 12 bits is plus/minus 0.125 error
16 bits is plus/minus 0.0078 error Music
CDs use 44.1 Kb rate and 16 bit encoding
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Sampling an analog voltage
Time
Voltage
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File size of regular Music CD (AAIF) song
files 44100 samples X 16 bits/ sample X 2
Channels, divided by 8 bits per byte X 60
seconds per minute 10.58375 Megabytes per
minute SO.. A 3 minute song is 31.5
Megabytes AND A 600 Mb blank CD can hold about
18 songs
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HOWEVER MP3 files are compressed to aprox
10 SO A CD can hold about 180 MP3 songs AND
Most new car radios will play MP3 CDs Thats
about 9 hours of music! OR Back Up your
Protected AACs (180 to the CD)
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Compressing Digital Music Will always
cause degradation, information is
lost Re-expansion cant recover lost
information Some compression algorithms are
better than others The human ear can be fooled
by smart algorithms Computation
considerations Processing power (time)
to compress Processing power (time) to
expand for playback
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MP3 and AAC (MP4) files MP3 compression at
128Kb/s to 9.4, at 192 Kb/s to 13,7 AAC
compression at 128 Kb/s to 9.4 But sounds
about same as MP3 at 192 Kb/s Apple uses AAC at
128 Kb/s for the iTunes Music store They also
added proprietary copy protection Called
Protected AAC or (M4P)
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Can you convert Protected AAC files
to Unprotected MP3 or AAC files? NOT directly,
but indirectly, YES iTunes WILL let you burn an
unprotected AAIF file to disk from an Protected
AAC file That AAIF can be re-imported as MP3 or
unprotected AAC Can you convert AAC files to MP3
? YES Can you convert MP3 files to unprotected
AAC files? YES So lets look at iTunes
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Preference settings File format
conversions Dragging songs to desktop for
burning with Toast
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In honor of our program chairman Alec
Whittaker, An Englishman, I selected Frank
Sinatras song A Foggy Day In London Town
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Demo files created 1. AAIF Original CD (23.3
Mb) 2. MP3 copy 1 (128Kb/s, 2.2 Mb) 3. MP3 copy
1 (192Kb/s, 3.2 Mb) 4. AAC copy 1 (128Kb/s, 2.2
Mb) 5. Expansion of AAC copy 1 (23.3
Mb) compress/expand/compress.. 6. Expansion
of AAC copy 9 (23.3Mb) 7. AAC copy10 (2.2 Mb)
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How do these files sound? Can YOU tell the
difference? Is the file size savings worth the
difference? Only how YOU feel with YOUR ears
matters Lets listen (blind at first)