Apple says that the 16GB 5th generation iPod nano can hold up to 4,000 songs, so it seems safe to assume that a 4GB model can hold about 1,000 songs. But’s not the whole story.
How many songs a 4GB iPod can hold depends on how the songs were encoded. Encoding is the process of taking music and converting to a digital format (or converting from one digital format to another).
Apple’s number is based on encoding the songs being four-minute-long 128 Kbps AAC format files.
The two major formats of music used on the iPod are AAC and MP3. In non-scientific comparisons, I found that AAC is generally creates a better sound, but is also a bigger file than the equivalent MP3.
Filesize is also determine by the bit rate of the file. Apple uses 128 Kbps as its baseline, but the higher the bit rate, the better the song will sound. For instance, all music from the iTunes Store is now offered in 256 Kbps.
If you’re ripping songs from CD, you can choose what file format and bit rate you want to encode songs using. Your choices will help determine how many songs a 4GB iPod can hold.
So, Apple’s claim of 4,000 songs is correct in some settings, but for those looking for better sound quality, the number will be less, depending on the quality of the encoding, the file format, and the length of the songs.