Raymond Steele

Embedding data in speech using scrambling techniques

A method of embedding data into speech signals is proposed. The speech signal is scrambled using the data as the scrambling key, while the receiver adopts the role of a code breaker. By judicious choice of scrambling algorithm the receiver can be made to break the code at every attempt. We found that 126 b/s can be transmitted without error over a channel whose additive noise is only 10 dB below the mean square value of the speech signal.

SNR Formula for Linear Delta Modulation with Band-Limited Flat and RC-Shaped Gaussian Signals

Easy to use simple equations of optimum slope loading factor and peak SNR are given for a linear delta modulator having Gaussian input signals with band-limited RC spectra. The equations are accurate to within 1 dB over a wide range of normalized sampling frequency and for RC spectrum bandwidths of practical interest.

Statistical Block Protection Coding for DPCM-AQF Speech

The statistical block protection coding scheme [2] for protecting DPCM encoded speech signals through noisy channels has been extended to accommodate DPCM-AQF encoded speech, where AQF stands for adaptive quantization with forward (explicit) transmission of step size. Signal-to-noise ratio (SNR) gains, typically 12 dB, have been achieved over a dynamic range > 20 dB for a bit error rate (BER) of 1.4 percent and the SNR improvement is found to increase with BER. Perceptual improvements in decoded speech have a good correspondence with the gains in SNR. The penalty for this substantial enhancement in the performance of the DPCM-AQF system is an increase in transmission bit rate of 3.5 percent and encoding delay of 64 ms.

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.