[nmithani1]

Whenever I download a song in VBR mp3 format, the filename of the song contains the text 'abr' in it. Allofmp3.com's assistance told me previously that the option is indeed VBR and not ABR. I myself have used LAME 3.97 through softwares such as dbPowerAMP and Easy CD-DA Extractor, and ABR and VBR are discrete options.

The more serious problem, however, is I downloaded "O Fortuna" by Carl Orff at 192 kb/s VBR (I've provided the link to the album below) but the file's bitrate turned out to be 177kb/s as measured by iTunes v6, Media Player Classic v6.4.9.0 and GSpot v2.70a.

http://www.allofmp3.com/r2/Various_A...mcatalog.shtml

What is going on?

[Cornutopian]

Originally Posted by nmithani1

Whenever I download a song in VBR mp3 format, the filename of the song contains the text 'abr' in it. Allofmp3.com's assistance told me previously that the option is indeed VBR and not ABR. I myself have used LAME 3.97 through softwares such as dbPowerAMP and Easy CD-DA Extractor, and ABR and VBR are discrete options.

The more serious problem, however, is I downloaded "O Fortuna" by Carl Orff at 192 kb/s VBR (I've provided the link to the album below) but the file's bitrate turned out to be 177kb/s as measured by iTunes v6, Media Player Classic v6.4.9.0 and GSpot v2.70a.

http://www.allofmp3.com/r2/Various_A...mcatalog.shtml

What is going on?

A vbr recording at 192KB isn't going to actually BE AT 192KB/s. VBR is variable and the 192 is the average that the encoder shoots for. But the ultimate determiner of bitrate is the complexity of the music, so every track will be slightly different.

At least that is MY understanding of it.

[nmithani1]

From my extensive experience with LAME 3.97 (through softwares such as dbPowerAMP and Easy CD-DA Extractor) VBR is the minimum bitrate setting with the instantaneous bitrate hovering above it when there is more audio data; ABR is average with the instantaneous bitrate rising and falling relative to the selected average value. Provided, one can set the range within which the bitrate may vary when selecting ABR and VBR but 177kb/s is too far. The maximum instantaneous bitrate of the file I downloaded was 185kb/s, if it was VBR then the minimum instantaneous bitrate should have been ~192kb/s, if it was ABR then the average instantaneous bitrate should have been ~192kb/s.

Use either dbPowerAMP or Easy CD-DA Extractor (this one has a better user-interface) for familiarisation.

[burninator88]

As Cornutopian said, VBR always gives some leeway to the encoder to choose the bit rate based on the complexity of the music at that moment. For example, a moment of absolute silence would be encoded at and extremely low bitrate while moments with very complex soundscapes will take up higher bitrates.

A couple of places where more efficient compression can happen are places where the audio shows 1) limited dynamic range (not going from loud to quiet but staying mostly at the same loudness) 2) limited bandwidth of the sound spectrum and 3) same or mostly similar audio in both the left and right stereo channels.

In a piece like O Fortuna you have all 3 of these. First, there is about a minute of pretty quiet singing and then it gets loud for the rest of the piece. This restricted dynamic range over long portions of the piece helps save some bandwidth. Second, the human voice has a notably restricted range in terms of Hertz (only a small fraction of the 20Hz-20,000Hz that is usually encoded by MP3). For long stretches of the piece (basically anywhere except for the cymbal crashes) I would imagine that there is practically no audio information above 10,000Hz. This is half of the spectrum and would take up a lot of information in an MP3 file. If it can be left out then it will reduce the overall bitrate. Thirdly, I would imagine that the recording is very similar between the left and right channels. It may even be in mono. This will cut down significantly on the size (and thus the bitrate) as well.

As an example I have two albums that I encoded myself using iTunes set to use MP3-VBR at the 320kbps (highest possible rate), using Joint Stereo. The first is Metallica (Black Album). The average bitrate of these songs, as shown by iTunes, is in the 220-230kbps range. The second album is Albinoni's Adagios (quiet classical pieces with limited instrumentation). These MP3s (remember, encoded with the same settings) run in the 170-180kbps range.

As another example I have the album "The Reminder" by the performer "Feist" that I just bought from MP3Sparks using the MP4 "Extreme" settings (average 220kbps). Most of the songs end up being slightly over 220kbps (one goes very high to 257kbps) while track #4, "The Park" which is sonically much simpler than the other songs on the album (just female vocals and guitar, no drums or other instruments) runs at just 175kbps.

I have other albums (that I personally encoded with CD-EX, which uses LAME) and I see similar differences between classical and popular pieces when using the same VBR encodings. It is just the nature of the signal that it is more compressible. Sometimes the codec just decides that there's no benefit to going any higher bitrate.