A method of encoding signal data, comprising: obtaining coefficient bits representing values for a set of transformed coefficients, the values being generated by applying at least a transform operation to blocks of signal data derived from an input signal being encoded; obtaining userdata bits representing custom data to add to an encoded signal bitstream; applying a bit shift operation to the coefficient bits, the bit shift operation shifting the coefficient bits by a predefined number of bits, wherein the predefined number of bits is either 2 or 6 bits; setting values of a set of additional bits added to the coefficient bits based on the userdata bits to generate a modified set of coefficient bits; and instructing generation of an encoded bitstream using the modified set of coefficient bits, wherein the encoded bitstream carries both the custom data and an encoding of the signal data, wherein the blocks of signal data comprise residual data generated by comparing data derived from the input signal being encoded and data derived from a reconstruction of the input signal, the reconstruction of the input signal being generated from a representation of the input signal at a lower level of quality, wherein the encoded bitstream is an encoded enhancement bitstream for a first enhancement sub-layer at a first level of quality, and the method further comprises: obtaining further coefficient bits representing values for a set of transformed coefficients at a second level of quality, the second level of quality being higher than the first level of quality, the values being generated by applying at least a transform operation to blocks of signal data at the second level of quality; and instructing generation of an encoded enhancement bitstream for a second enhancement sub-layer at the second level of quality using the further coefficient bits without applying a bit shift operation. obtaining coefficient bits representing values for a set of transformed coefficients, the values being generated by applying at least a transform operation to blocks of signal data derived from an input signal being encoded; obtaining userdata bits representing custom data to add to an encoded signal bitstream; applying a bit shift operation to the coefficient bits, the bit shift operation shifting the coefficient bits by a predefined number of bits, wherein the predefined number of bits is either 2 or 6 bits; setting values of a set of additional bits added to the coefficient bits based on the userdata bits to generate a modified set of coefficient bits; and instructing generation of an encoded bitstream using the modified set of coefficient bits, wherein the encoded bitstream carries both the custom data and an encoding of the signal data, wherein the blocks of signal data comprise residual data generated by comparing data derived from the input signal being encoded and data derived from a reconstruction of the input signal, the reconstruction of the input signal being generated from a representation of the input signal at a lower level of quality, wherein the encoded bitstream is an encoded enhancement bitstream for a first enhancement sub-layer at a first level of quality, and the method further comprises: obtaining further coefficient bits representing values for a set of transformed coefficients at a second level of quality, the second level of quality being higher than the first level of quality, the values being generated by applying at least a transform operation to blocks of signal data at the second level of quality; and instructing generation of an encoded enhancement bitstream for a second enhancement sub-layer at the second level of quality using the further coefficient bits without applying a bit shift operation. obtaining further coefficient bits representing values for a set of transformed coefficients at a second level of quality, the second level of quality being higher than the first level of quality, the values being generated by applying at least a transform operation to blocks of signal data at the second level of quality; and instructing generation of an encoded enhancement bitstream for a second enhancement sub-layer at the second level of quality using the further coefficient bits without applying a bit shift operation.