Editing Delta modulation (section)

== Asynchronous delta modulation ==
The 1947 Deloraine, 1950 Cutler, and 1952 Jager designs were [[Synchronous circuit|synchronous]] (or time-quantized). Delta modulation is also possible without a fixed sampling rate. A February 1966 paper by H. Inose "Asynchronous delta-modulation system"<ref>{{Cite journal |last1=Inose |first1=H. |last2=Aoki |first2=T. |last3=Watanabe |first3=K. |date=March 1966 |title=Asynchronous delta-modulation system |url=http://digital-library.theiet.org/doi/10.1049/el%3A19660077 |journal=[[Electronics Letters]] |language=en |volume=2 |issue=3 |pages=95–96 |doi=10.1049/el:19660077 |bibcode=1966ElL.....2...95I |issn=0013-5194}}</ref> uses [[Schmitt trigger|Schmitt triggers]] to detect when the input signal exceeds the local demodulator by a predetermined difference, with the benefit of reducing the number of output pulses. A November 1973 paper "Signal Coding Using Asynchronous Delta Modulation" (presented in 1974)<ref>{{Cite journal |last1=Hawkes |first1=T. |last2=Simonpieri |first2=P. |date=March 1974 |title=Signal Coding Using Asynchronous Delta Modulation |url=https://ieeexplore.ieee.org/document/1092185 |journal=[[IEEE Transactions on Communications]] |volume=22 |issue=3 |pages=346–348 |doi=10.1109/TCOM.1974.1092185 |issn=0090-6778}}</ref> investigates an algorithm that varies the sampling rate to transmit fewer samples during periods of small signal variation.