The input waveform is analyzed, and if there is a significant transient in the second half of the block, the waveform will be split into two to prevent pre-echo. In this case, the number of coefficients remains the same, but the frequency resolution will be halved and the temporal resolution will be doubled. A flag is set in the bit stream to indicate to the decoder that this has been done. The coefficients are output in floating-point notation as a mantissa and an exponent. The representation is the binary equivalent of scientific notation.
Exponents are effectively scale factors.
The set of exponents in a block produce a spectral analysis of the input to a finite accuracy on a logarithmic scale called the spectral envelope. This spectral analysis is the input to the masking model that determines the degree to which noise can be raised at each frequency. The masking model drives the requantizing process, which reduces the accuracy of each coefficient by rounding the mantissae. A significant proportion of the transmitted data consist of these mantissae. The exponents are also transmitted, but not directly as there is further redundancy within them that can be exploited.