Formant locating system

Abstract

Abstract 1,034,757. Speech recognition apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. April 5, 1965 [May 18, 1964], No. 14262/65. Heading G4R. In apparatus for determining the frequency of a resonant peak in a signal having a wide frequency band, the logarithm of the power in each of a number of frequency channels is measured, the measurements are weighted and linearly combined and the resulting signal fed to an indicator adapted to indicate the frequency of the or each peak. In the form described, the signal from source 10, Fig. 5A (not shown), is split into 36 channels by band-pass filters 20-1 to 20-36. The output of each filter passes to a square-law detector 30-1 &c. to derive a signal representing the power in the corresponding channel. After smoothing at 40-1 &c. the logarithm of the power signal is obtained at 50-1 &c. The 36 log. power signals pass to each of 55 linear combinors 60-1 &c., Fig. 5B (not shown). Each of the incoming signals is weighted by a potential divider 70-1 &c., Fig. 6 (not shown), and the weightings are adjusted so that the combined output signal is a voltage proportional to the numoer of formants below a specified frequency. Each linear combinor circuit 60-1 &c. has a different specified frequency. If there is one formant below the given frequency an output of 1 volt is obtained, 2 volts for 2 formants and 3 volts for 3 formants. The outputs of each combiner circuits 60-1 &c. is applied to the three threshold devices 81-1 &c., 82-1 &c., Fig. 5C (not shown), and 83-1 &c., Fig. 5D (not shown), having levels 0À5 v.,1À5 v. and 2À5 v. Those combiner circuits indicating that there is one formant below the corresponding frequency give an output from the associated threshold device 81-1 &c. Those indicating two formants give an output from threshold device 82-1 &c. and those indicating three formants give an output from threshold devices 83-1 &c. The exact frequency of these formants is found by inverting the output from each threshold device and gating it with the output from the one above. The gates 101-1 &c., 102-1 &c., 103-1 respond to indicate the frequency band in which lie the first, second and third formants. Indicators 111-1 &c., 112-1 &c. and 113-1 &c. may be printers, lamps or counters.

Inventors

• 👤 Bakis Raimo

Bibliographic Details