Backwards adaptation

The basic waveform coders presented so far compute and transmit LPC and residual parameters on a frame by frame basis. Backwards adaptation uses past decoded speech to estimate the LP model. Issues are:

• No need to transmit LP paramterers
  • LP Model is poorer - trained on delayed data
  • LP paramters are hard to quantise - consume appreciable bandwidth
  • Simpler bitstream format
• Longer model order is possible - not limited by quantisation error
• Decoder needs more power to generate the LP model

Works best for low delay systems.