Reader Gino Vogt ’s interrogative earmark me to wear two hats — one asMacworld’sMac 911 cat and the other as the host of Macworld ’s podcast . He write :
Gino , I ’d like to think that our podcast justreeksof quality , but my signified is that you ’re not talking about the contentedness . This compression / quality hooey can be perplexing . permit me excuse .
Bit - rate — the number of act per second used to encode audio , which is represent in kilobits per second ( kbps)—is the determine factor . The gamey the bite - rate , the larger the file size and , generally , the better the caliber . However …
Quality vary among encoders . Apple claims that an AAC file cabinet encoded at 128kbps sounds better than an MP3 Indian file encoded at the same act - rate ( and as good as an MP3 file encoded at 160kbps ) . This explicate why , when Apple interchange iTunes ’ default encryption format to AAC at 128kbps from MP3 at 160kbps , iPods were publicise to agree more music than they could previously . A 160kbps Indian file — whether MP3 or AAC — wipe out the same amount of surd drive space . But make iTunes pull at 128kbps and suddenly the size of a 4 - hour track goes from 4.1 megabyte to around 3.7 MB .
Okay , so we get that a 128kbps AAC file and a 128kbps MP3 file cabinet are live to eat the same amount of blank space . In that case , what ’s lead on with our podcast files ?
We ’re using the same bit - rate for both the AAC and MP3 version—32kbps , mono . I would n’t dream of encode music at such a low chip - rate , but for speech , it ’s a perfectly fine compromise — peculiarly when you consider how long it would take to download 45 minutes of audio recording encoded at euphony - quality ( and what it would cost to host such large files ) .
So what explains the somewhat bulkier AAC version ? It ’s a mite larger because it ’s an enhanced podcast — one that includes ikon , links , and chapters .
