What is Musicam

Musicam, also known as MPEG-1 Audio Layer II or MP2, is a lossy audio codec defined by the ISO/IEC 11172-3. MP2 is mostly used in the field of audio broadcasting. DVB and DSS both use Musicam as their primary audio format.

The Technical Specifications of Musicam

ISO/IEC 11172-3 is used to define MPEG-1 Layer II or Musicam. It has the following specifications:

• Sampling Rates: 32, .1 and 48 kHz
• Bitrates: 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320 and 384 kbit/s

Aside from the specifications stated above, an extension has been provided in MPEG-2 Layer II for Musicam. These specifications are defined in ISO/IEC 13818-3

• Additional sampling rates: 16, 22/05 ad 24 kHz
• Additional bitrates: 8, 16, 24, 40 and 144 kbit/s

The format for Musicam is based on 1152 different sampling intervals for successive digital frames. The four possible formats for Musicam are:

• Mono format
• Stereo format
• Joint stereo format for stereo irrelevance
• Dual channel or uncorrelated format

How Musicam works

Musicam is a sub-band audio encoder. This means that the audio compression takes place in the particular time domain with a low-delay filter bank producing 32 frequency domain components. The algorithms and formats used in Musicam are the prototype for the structures used in MP3 codec. The Musicam encoder exploits redundancies of the inner channel depending on the mode for encoding. It may also use similar encoding procedures with the MP3 stereophonic mode when using its Joint Stereo coding mode. Musicam performs similar toMP3 on higher bitrates and are more resilient to errors. The codec used for Musicam removes information that the human ear may not perceive. The audio signal is analyzed based on a psychoacoustic model with parameters similar to those of the human auditory system. Frequency masking is used to remove imperceptible frequencies, which allows increased allocation of data to recreate perceptible frequencies. Musicam splits the processed audio signal to 32 different sub-bands. Musicam shows better behavior compared to MP3 because of its lower frequency resolution and reduced time delay for codec. The sub-band filter bank of Musicam masks the filters unused or unneeded to produce an audio signal.

Musicam and its applications

Musicam is used internally in the programming distribution system of the radio industry as well as the DAB digital radio and DVB digital television standards. DVD-Video players using the PAL system contains stereo Musicam decoders as well.