On the Voyager 1 inbound pass through the Jovian magnetosphere, the frequent acquisition of wide band data from the plasma wave instrument has permitted a quasi-continuous survey of the waves which occur in the frequency band below the electron cyclotron frequency, the chorus band. Structured, rising frequency chorus was observed just outside the dense Io plasma torus but inside the low-density middle magnetosphere. A quasi-continuous, very narrow band emission occurred just above one-half the electron cyclotron frequency. Power spectra, which were constructed from the wide band data, showed that the half-cyclotron emission is unaffected by the simultaneous occurrence of chorus at lower frequencies and is separated from the chorus by a deep spectral gap just below one-half the cyclotron frequency. Within the rising chorus band, a hisslike emission was observed which consisted of two quasi-continuous, very narrow band tones located near the upper and lower frequency limits of the rising chorus band. Sequential power spectra showed that these twin-frequency tones persisted during rising chorus bursts. Chorus occurs in the spatial regions where whistlers have cyclotron resonant interactions with the suprathermal population of ~keV electrons. A possible interpretation of the twin tones is that these signals are electrostatic or resonance cone whistlers. Growth rate calculations show that the electrostatic whistler is destabilized by a low cone distribution with the same pitch angle anisotropy which is needed to excite the electromagnetic chorus whistlers. A speculative hypothesis is presented to explain the half-cyclotron emission. The Landau absorption of oblique chorus whistlers results in the spectral gap just below one-half the cyclotron frequency and in the formation of a quasi-linear plateau in the parallel velocity distribution of the suprathermal electrons. The plateau alters the Landau and cyclotron resonant interactions and permits the unstable growth of electrostatic and electromagnetic whistlers in a narrow range just above one-half the cyclotron frequency.