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1loser
6th February 2002, 15:01
What is the difference between mp2 and mp3?

When would you use mp2 vs mp3?

I read in a post that TMPGEnc uses mp2 to make a VCD but I thought I was able to successfully use mp3 when creating a VCD.

sibe
6th February 2002, 16:36
Simply put, mp2 is the predecessor of mp3, so mp2 is an older audio format. But because the (S)VCD standart uses mp2 you need this to create these kinds of disks.

I think it's possible to create a VCD with mp3 audio, but I don't know if there are any standalone players who support this, because it's non-standart.

Sibe

LigH
6th February 2002, 18:54
As far as I remember, at least MPEG-1 Layer 2 audio (MP2) does not use such complex algorithms to ignore unrecognised frequencies (psycho-acoustic analysis), therefore it requires more bitrate than Layer 3 audio, but is easier to implement in hardware and faster to decompress. I'd recommend to ask authors of MP3 encoders or decoders, they shall know best.

tangent
7th February 2002, 08:51
Both MP2 and MP3 go through the same first process where the original frame of 1152 samples (for long blocks) is decomposed into 32 subbands of equal frequency bandwidths. After this, the two codecs split off into two different paths.

For MP2, a 1024 point FFT is applied to the entire window to perform the frequency analysis for the psychoacoustic engine. Masking curve is calculated, and the power of each subband is examined. If the entire subband falls under the masking curve, then the whole subband is not encoded. Bits are then allocated to each subband according to the Signal-to-Mask ratio, then each subband is normalised and quantised according to the bits provided.

For MP3, an 18-point MDCT is applied to each subband. This provides both the spectrum analysis and the coefficients to encode. The psychoacoustics engine decides which coefficients are audible (falls below the masking curve) and which are not and encodes just the ones which are audible.

In general, MP3's encoding is more efficient and allows for decent quality at the bitrates of around 128kbps. However at the higher bitrates of >256kbps, I expect MP2 to be as good as, if not better than MP3 because MP2 doesn't suffer from the pre-echo effects which MP3 (as well as other transform coders) always suffer from.

DSPguru
7th February 2002, 09:06
layer3 also includes an entropy encoder (huffman).