Audio Compression for Spoken Word (Audio Books)

When renting a book on CD from the library, I often find I cannot listen to the entire book before its due date (any of the Harry Potter books are a good example as they’re all over 15 CDs long). Combine CDex (freeware CD ripping software) with LAME (freware MP3 encoder), and you can rip the book to your hard drive or MP3 player. Further combine with some acceptable loss in audio quality for spoken word, and space is no longer a problem to hold that entire audio book on your mp3 player…

Just be sure to delete it once you’re done; it’s the library’s copy, NOT YOURS.

Recommended Compression Settings

• Downmix to Mono (2:1)
• Downsample to 16 kHz (~ 3:1)
• Encode using VBR (max setting) (~ 9:1)

Audio Compression examples

• 8.4sec Original CD Track Audio Clip
  (44.1khz, Stereo, 16bit) (1.4 MByte)
  
• 8.4sec Converted to Mono
  (44.1kHz, Mono, 16bit) – 2:1 compression ratio (723 KByte)
  
• 8.4sec Converted to MP3
  (16kHz, Mono, VBR 8kHz-160kHz, LAME-encoded) – >50:1 compression ratio (25.4 KByte)
  
• Downloadable examples:
  – original (stereo)
  – original (mono)
  – mp3 compressed
  – mp3 compressed but saved as .wav for online playback compatibility

Example Using Above Settings

Harry Potter, H.B.P. (JK Rowling), 17 CDs
– RAW Size:  11,200 MByte
– Compressed: 213 MByte
– Compression Ratio: 52 : 1