Circuit for automatic selection between speech and music sound signals

Electric circuit for automatic switching of a sound reproduction and signal apparatus for exercising a selected choice, among selectable signals, between speech and music sound reproduction signals, comprising:

• means (40) for registering said selected choice;
• means (12,13) for subjecting a selectable or selected sound reproduction signal, to be tested for conformance with a choice registered in said registering means, to separation of said signal into a low-frequency signal component and a high-frequency signal component, said low-frequency signal component containing substantially all component frequencies of said sound reproduction signals which are less than 3 kHz;
• means (14-19) for converting said low-frequency and high-frequency signal components respectively into first and second sequences of amplitude-limited pulses;
• first timing means (24) responsive to said first sequence of amplitude-limited pulses for detecting pauses in said low-frequency signal component which pauses exceed a first predetermined duration;
• second timing means (25) for identifying periods of time in which said pauses detected by said first timing means succeed each other at intervals not exceeding a second predetermined duration;
• third timing means (26) responsive to said second sequence of amplitude-limited pulses for detecting the occurrence of pauses in said high-frequency signal component exceeding a third predetermined duration which is less than said first predetermined duration;
• fourth timing means (23) responsive to said first sequence of amplitude-limited pulses for detecting the occurrence of pauses in said low-frequency signal component exceeding a fourth predetermined duration which is longer than said third predetermined duration and shorter than said first predetermined duration;
• first logic circuit means (27,27a) responsive to the outputs (a,d) of said first and fourth timing means for detecting the absence of a pause exceeding said third predetermined duration in said high-frequency signal component during the portion of a pause in said low-frequency signal component which exceeds said fourth predetermined duration and thereby producing a first logic output signal (e) and for detecting the absence of a pause exceeding said third predetermined duration in said high-frequency signal component during the absence of pauses exceeding said fourth predetermined duration in said low-frequency signal component and thereby producing a second logic output signal (f);
• second logic circuit means (31) for dientifying a music signal by a third logic output signal (h) with reference to the respective states of said first and second logic output signals (e,f) and the state of the output (c) of said second timing means (25) and for identifying a speech signal by a fourth logic signal (i) with a reference to the respective states of said first and third logic signals (e,h) and the respective states of the outputs (b,c) of said first and second timing means (24,25), and
• sound reproduction signal evaluating means (33-39) for comparing the state of said registering means (40) with the corresponding one of said third and fourth logic signals and determining in response thereto whether or not the sound reproduction signal selected for test is of the character selected by said registering means.