CBR vs VBR Encoding

Trade between audio quality and file size

To rip your music CDs to an audio format like MP3, WMA, AAC, etc., or to convert between formats, it's a good idea to know what CBR and VBR mean before you start.

  • Fixed quality

  • Guaranteed higher quality files

  • Quicker encoding

  • Wider compatibility

  • Smaller file sizes

  • More efficient use of storage space

  • Minimal reduction in quality

  • Possibly more limited support

There are a multitude of factors that impact the quality of your digital music library. Bitrate is one of them. Whether you're looking to get the absolute best quality rips or you're trying to maximize space on your mobile device, it's important to weigh your options in choosing the bitrate.

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CBR Encoding

  • Set quality

  • More control over the audio quality

  • Better for multimedia

  • Requires a connection to support it

  • Inflexible

CBR stands for constant bitrate, and is an encoding method that keeps the bitrate the same; VBR, by contrast, is variable bitrate. When audio data is encoded by a codec, a fixed value is used, like 128, 256 or 320 Kbps.

In general, the higher the bitrate, the better the quality of the audio.

The advantage of using the CBR method is that audio data typically processes faster compared to the alternatives. However, the files that are created aren't as well optimized for quality-versus-storage as is the case with VBR.

CBR is useful for streaming multimedia files. If the connection is limited to only performing at, say, 320 Kbps, then a constant bitrate of 300 Kbps per second or lower would be more beneficial than one that changed throughout the transmission since it could possibly go higher than what's allowed.

VBR Encoding

  • Smaller file size

  • Flexible reduction in bitrate

  • More efficient in many situations

  • Possible decreases in quality

  • Less widely supported

  • Longer to encode

VBR allows the bitrate of an audio file to dynamically increase or decrease within a target range; the LAME encoder, for example, varies between 65 Kbps and 320 Kbps.

Like CBR, audio formats such as MP3, WMA, OGG, etc support VBR.

The biggest advantage of VBR when compared to CBR is the sound-quality-to-file-size ratio. You can usually achieve a smaller file size by encoding audio with VBR than CBR because of the way bitrate is altered depending on the nature of the sound.

The bitrate reduces for silence or quieter parts of a song. For more complex areas of a song that contain a mix of frequencies, the bitrate increases (up to 320 Kbps) to ensure sound quality is maintained. This variation in bitrate will, therefore, help to reduce the storage space needed compared to CBR.

However, the disadvantage of VBR encoded files is that they might not be compatible with older electronic devices like CBR is. It also takes longer to encode audio using VBR because the process is more complex.

Which One Should You Choose?

Unless you're restricted by old hardware that only supports audio formats encoded using CBR, then VBR is usually the recommended method. Support for VBR in hardware devices like MP3 players, PMPs, etc., used to be hit and miss, but these days it's usually a standard feature.

VBR gives you the best balance between quality and file size. It's therefore ideal for portables that have limited storage or where you want to make efficient use of other storage solutions like USB flash drives, flashcards, etc.