Nokia N91 User's Guide download pdf (Page 27)

Music player

Change album art

1 Select a song.

2 Select Options > Album art.

3 Select Options > Change.

4 Scroll through images from your Gallery, and select

Select:.

5 To restore the original album art, select Restore original.

About encoded audio

Applications like Windows Media player and Nokia Audio

Manager encode audio files with codecs like WMA or MP3

to save storage space. The encoding is done by removing

those parts of the audio signal that are not audible or only

barely audible by human ear.

Regardless of the encoder and codec quality, the sound

quality of the resulting file is not as good as the original.

The basic codecs supported by this device are AAC, WMA,

and MP3. All of these have different variations.

Bitrates

When encoding audio, the quality of the resulting sound

depends on the sample rate and bit rate used for the encoding.

Sample rate is expressed as thousands of samples per

second (kHz), and for CD music the sample rate is fixed at

44.1 kHz. Bit rate is expressed as kilobits per second (kb/s).

The higher the bitrate, the better the sound quality.

The required quality level may depend on your demands,

the headphones used, and the surrounding noise. For MP3s

a bitrate between 128 and 192 kb/s usually gives results

good enough for listening to pop music with your device.

WMA or AAC generally gives a similar result as MP3 with

one step lower bitrate (96-160 kb/s). Variations of AAC,

such as AAC+ and enhanced AAC+ (eAAC+) provide CD

quality audio at bitrates as low as 48 kb/s. Classical music

and music with nuances usually require a higher bitrate

than basic pop music.

For speech or other sources where the quality of the sound

is less important than saving storage space, you can use

bitrates between 8 and 64 kb/s. At low bitrates WMA

or AAC generally gives better results than MP3.

Variable bitrate

Your device also supports variable bitrate (VBR). Variable

bitrate means that the bit rate of the encoding varies with

the complexity of the encoded material. When using VBR,

the encoding is optimized to preserve a constant audio

quality throughout the track, rather than losing quality

for complex music sections as with constant bitrate

(CBR) encoding.

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Nokia N91 User's Guide Page 27

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