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Additional improvements were introduced by [[quadrature amplitude modulation]] (QAM) encoding, which increased the number of bits per symbol to four through a combination of phase shift and amplitude.
Transmitting at 1,200 baud produced the 4,800 bit/s [[V.27ter]] standard, and at 2,400 baud the 9,600 bit/s [[V.32]]. The [[carrier frequency]] was 1,650 Hz in both systems.
The introduction of these higher-speed systems also led to the development of the digital [[fax]] machine during the 1980s. While early fax technology also used modulated signals on a phone line, digital fax used the now-standard digital encoding used by computer modems. This eventually allowed computers to send and receive fax images.
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In the early 1990s, V.32 modems operating at 9,600 bit/s were introduced, but were expensive and were only starting to enter the market when V.32bis was standardized, which operated at 14,400 bit/s.
[[Rockwell International]]'s chip division developed a new driver chip set incorporating the [[V.32bis]] standard and aggressively priced it. [[Supra, Inc.]] arranged a short-term exclusivity arrangement with Rockwell, and developed the [[SupraFAXModem 14400]] based on it. Introduced in January 1992 at {{US$|long=no|399}} (or less), it was half the price of the slower V.32 modems already on the market. This led to a price war, and by the end of the year V.32 was dead, never having been really established, and V.32bis modems were widely available for {{US$|long=no|250}}.
V.32bis was so successful that the older high-speed standards had little advantages. USRobotics (USR) fought back with a 16,800 bit/s version of HST, while AT&T introduced a one-off 19,200 bit/s method they referred to as ''V.32ter'', but neither non-standard modem sold well.
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