Slope limiting filters for enhancing noisy channel performance of codecs

This paper explores the use of slope limiting filters to mitigate the errors induced in adaptive and non-adaptive PCM and DPCM speech. The two correctors discussed use slope limiting to remove the spikes associated with bit errors. They are treated as add-on systems with no knowledge of the input signal other than that it is a speech waveform, and use very simple replacement algorithms when they detect an anomalous condition. The methods do not make an "optimum" replacement of anomalous conditions; however, simple replacement algorithms result in significant improvement of corrupted speech, especially where listening fatigue is a factor. They use inexpensive (analog and delta modulation) circuits which are easily constructed and installed.