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MPEG AND DSP INTEGRATION

by Priyesh Surati & David Austin

Start ý MPEG Audio Encoding and Decoding ý Encoder Technology ý Decoder Technology ý Affect on the Music Industry ý Current Uses ý Sources and PDF

DECODER TECHNOLOGY

The decoder is a computer algorithm that converts the MP3 file format to a WAV file capable of being played on a soundcard or other audio device (see Figure 6).

Figure 6ýHere you can see the various blocks of the decoder and how they interact with each other.

The decoder works by taking in a bitstream, using the reverse process of the encoder. First, the bitstream is decoded, then reduced, and finally, the Inverse Fast Fourier Transform (IFFT) is applied. The IFFT converts the signal back to the time domain, where it can then be played on a soundcard or other sound device.

COMPLEXITY OF THE DECODER

The decoder complexity is directly related to the type of file format it will decode. Like the encoder, the complexity increases as the layer increases, so a Layer I decoder is simpler than a Layer III decoder. To meet the MP3 decoder standard, a decoder must be backward compatible. Therefore, if a decoder states it decodes MPEG-1 Layer III, it must also decode Layer I and II. [2]

SOUND QUALITY

After the data is encoded, the decoder can decode a variety of sound qualities. These qualities can range from telephone sound to CD-quality (see Table 2).

Table 2 shows how sound quality and bit rate are both directly related to bandwidth. Most of the time, bandwidth is a limiting factor in a communication system. This is why the phone system sounds so poor. The sound you hear in the phone system uses just enough bandwidth to allow individual voices to be distinguished. [6]

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