Editing MPEG-1 Audio Layer II (section)

==Technique==
{{See also|MPEG-1#Layer II}}

MP2 is a [[sub-band coding|sub-band audio encoder]], which means that compression takes place in the [[time domain]] with a low-delay filter bank producing 32 frequency domain components. By comparison, [[MP3]] is a [[Audio data compression#Transform domain methods|transform audio encoder]] with hybrid filter bank, which means that compression takes place in the [[frequency domain]] after a hybrid (double) transformation from the time domain. MPEG Audio Layer II is the core algorithm of the MP3 standards. All psychoacoustical characteristics and frame format structures of the MP3 format are derived from the basic MP2 algorithm and format.

The MP2 encoder may exploit inter channel redundancies using optional "joint stereo" [[Joint stereo#Intensity stereo coding|intensity encoding]]. Like MP3, MP2 is a perceptual coding format, which means that it removes information that the human auditory system will not be able to easily perceive. To choose which information to remove, the audio signal is analyzed according to a psychoacoustic model, which takes into account the parameters of the human auditory system. Research into [[psychoacoustics]] has shown that if there is a strong signal on a certain frequency, then weaker signals at frequencies close to the strong signal's frequency cannot be perceived by the human auditory system. This is called frequency masking. Perceptual audio codecs take advantage of this frequency masking by ignoring information at frequencies that are deemed to be imperceptible, thus allowing more data to be allocated to the reproduction of perceptible frequencies.

MP2 splits the input audio signal into 32 sub-bands, and if the audio in a sub-band is deemed to be imperceptible then that sub-band is not transmitted. MP3, on the other hand, transforms the input audio signal to the frequency domain in 576 frequency components. Therefore, MP3 has a higher frequency resolution than MP2, which allows the psychoacoustic model to be applied more selectively than for MP2. So MP3 has greater scope to reduce the bit rate.

The use of an additional [[entropy coding]] tool, and higher frequency accuracy (due to the larger number of frequency sub-bands used by MP3) explains why MP3 does not need as high a bit rate as MP2 to get an acceptable audio quality. Conversely, MP2 shows a better behavior than MP3 in the time domain, due to its lower frequency resolution. This implies less codec time delay&nbsp;— which can make editing audio simpler&nbsp;— as well as "ruggedness" and resistance to errors which may occur during the [[digital recording]] process, or during transmission errors.

The MP2 sub-band filter bank also provides an inherent "[[Transient (acoustics)|transient]] concealment" feature, due to the specific temporal masking effect of its mother filter. This unique characteristic of the MPEG-1 Audio family implies a very good sound quality on audio signals with rapid energy changes, such as percussive sounds. Because both the MP2 and MP3 formats use the same basic sub-band filter bank, both benefit from this characteristic.