Referring to a modulation technique that impresses two bits on a baud, so that the bit rate is double the baud rate. Such a technique employs four signal states. Quadrature phase-shift keying (QPSK) is a dibit technique achieved by defining four phase shifts separated by 90 degrees. Quadrature amplitude modulation (QAM) is an amplitude modulation (AM) scheme in ISDN BRI that yields the same result.There are similar frequency modulation (FM) schemes, as well. See also AM, baud, baud rate, bit, bit rate, BRI, FM, QAM, QPSK, quadbit, signal, tribit, and unibit.