Abstract:
The invention relates to a cellular phone terminal system, and in particular to a method for changing timbre of a voice signal during conversation in a cellular phone terminal system having a filter for filtering a PCM input signal. The method comprises the steps of: waiting for a timbre selector key input for a desired timbre when a timbre converter key is inputted during conversation; and setting a filter coefficient of the filter correspondingly to the timbre selector key input and filtering the PCM signal to change timbre.

Description:
PRIORITY 
     This application claims priority to an application entitled “METHOD FOR CHANGING TIMBRE DURING CONVERSATION IN PORTABLE TELEPHONE” filed with the Korean Industrial Property Office on Dec. 30, 1999 and assigned Ser. No. 1999-65748, the contents of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a cellular telephone terminal, and in particular to a method for changing timbre of a voice signal during conversation in a cellular telephone terminal. 
     2. Description of the Related Art 
     In general, a vocoder of a cellular phone terminal has a filter, for example an FIR (Finite Impulse Response) filter, to improve timbre of voices which are transmitted and received during conversation. In other words, a filter coefficient of the FIR filter is suitably changed and the transmitted/received voices are accordingly equalized to improve the timbre. 
     However, the FIR filter provided in conventional cellular telephone terminals has been typically used only for improving the timbre during conversation, thereby degrading the efficiency of the source. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a method for changing timbre during conversation in a cellular telephone terminal. 
     To achieve the object of the invention, there is provided a method for changing timbre of a cellular telephone terminal having a filter for filtering a PCM input signal, said method comprising the steps of: waiting for a timbre selector key input for a desired timbre when a timbre converter key is inputted during conversation; and setting a filter coefficient of the filter correspondingly to the timbre selector key input and filtering the PCM signal to change timbre. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the internal structure of a cellular telephone terminal for performing functions according to a preferred embodiment of the invention; 
     FIG. 2 is a block diagram for showing the internal structure of a speech processing unit shown in FIG. 1; 
     FIG. 3 is a diagrammatic view for showing the structure of a 14-tap FIR filter shown in FIG. 2; and 
     FIG. 4 is a flow chart for showing a timbre changing process according to a preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the invention will be described in detail in reference to the accompanying drawings. It should be understood that like reference numbers are used to indicate like elements even in different drawings. Detailed descriptions of known functions and configurations that may unnecessarily obscure the aspect of the invention have been omitted. 
     FIG. 1 is a block diagram showing the internal structure of a cellular telephone terminal for performing functions according to a preferred embodiment of the invention. 
     A control unit  111  controls the overall operation of the cellular telephone terminal. A memory  113  stores control programs of the cellular telephone terminal and controls data generated under the control of the control unit  111 , and in particular filter coefficients of an FIR filter which are variously set according to each of timbres such as low, middle, high, middle low, middle high, original timbres, etc. 
     A key input unit  115  has a number of dialing digit keys, a menu key, a send key, etc, and generates key signals corresponding to selected keys by the user to send the same to the control unit  111 . 
     A voice memory  117  stores a number of voice messages. When a voice message is read out from the voice memory  117  under the control of the control unit  111 , a speech processing unit  119  processes the voice message into an analog signal and outputs the message via a speaker. Also, the speech processing unit  119  processes analog voices of the user inputted via a microphone into digital signals, and demodulates and outputs the received voice signals from a calling party or the called party to a telephone call. 
     A transmitter unit  121  receives the signals generated from the control unit  111  and modulates the same into digital signals to send to a duplexer  123 . The duplexer  123  transmits the radio signals received from the transmitter unit  121  via an antenna, and sends signals received via the antenna to a receiver unit  125 . The receiver unit  125  demodulates the radio signals received from the duplexer  123 , and sends the demodulated signals to the control unit  111 . The control unit  111  controls conversation in response to the received signals. 
     A display unit  127  is realized by LCD (Liquid Crystal Display), LED (Light Emitting Diode) or etc., and displays input data and control data from of the cellular telephone terminal which is processed under control of the control unit  111 . 
     FIG. 2 is a block diagram for showing the internal structure of a speech processing unit shown in FIG.  1 . 
     First, when a radio signal such as an EVRC (Enhanced Variable Rate CODEC) signal is received via the duplexer  123  from the counter part to the telephone call, the received signal is demodulated in the receiver unit  125  and into a voice in the speech processing unit  119  under control of the control unit  111 . The voice control unit  119  is comprised of an EVRC decoder  211 , a 14-tap FIR filter  213  and a CODEC  215 . 
     The signal demodulated via the receiver unit  125  is inputted into the EVRC decoder  211 , which processes an EVRC decoding on the demodulated signal and then outputs the decoded signal to the 14-tap FIR filter  213 . The 14-tap FIR filter  213  receives and filters the signal from the EVRC decoder  211  to convert the same in PCM (Pulse Coded Modulation), and then sends the converted PCM signal to the CODEC  215  thereby outputting an analog-modulated voice. 
     FIG. 3 is a diagrammatic view showing the structure of the 14-tap FIR filter shown in FIG.  2 . 
     The FIR filter used in FIG. 3 has a 14-tap structure, in which the filter coefficients are expressed in the following equation 1: 
     
       
         [ Cn]=C[ 13 −n]   
       
     
     Herein, [Cn] is a filter coefficient according to the number of the tap, and n is 0 to 13 in the 14-tap structure. 
     Also, x[n] indicates input data into the 14-tap FIR filter  213 , and y[n] indicates output data from the 14-tap FIR filter  213  after filtered therefrom as shown in FIG.  3 . 
     In this way, each of the filter coefficients corresponding to each of the low, middle, high, middle low, middle high and original timbres are set from the filter coefficients from [C1] to [C13] and stored in the memory  113 . Here, a timbre selector key is designated together with the filter coefficients which correspond to each of the timbres respectively. For example, the voice selector key is designated “1” when the filter coefficient of the low voice is [C1], and the voice selector key is designated “2” when the filter coefficient of the middle timbre is [C3]. 
     FIG. 4 is a flow chart for showing a timbre changing process according to a preferred embodiment of the invention. 
     First, during an established telephone conversation, at step  311 , the control unit  111  proceeds to step  313  when provided with a key signal from the key input unit  115  during processing of the conversation. In step  313 , the control unit  111  determines if the key signal from the key input unit  115  is a timbre converter key signal. Here, the timbre converter key means a key which is set by combination of a number of keys provided in the key input unit  115 , which is inputted to select a timbre which is desired for conversion of the voices transmitted and received during conversation. 
     When it is determined that the key signal is not the timbre converter signal, the control unit  111  proceeds to step  315 . In the step  315 , the control unit  111  performs an operation corresponding to the inputted key. 
     If it is determined that the key signal is the timbre converter key signal, the control unit proceeds to step  317 . In the step  317 , the control unit  111  determines if the timbre selector key signal is applied from the key input unit  115 . Here, the timbre selector key means a key which is set by combination of the number of keys provided in the key input unit  115 , which is inputted to select a timbre which is desired for voice conversion such as one of low, middle, high, middle low, middle high and original timbres corresponding to the input of the timbre convert key. If the timbre selector key signal is not provided during a previously set time period as a result of the inspection, the control unit  111  processes the step as an error. 
     The control unit  111  proceeds to step  319  if the timbre selector key signal has been provided. In step  319 , the control unit  111  checks memory  113  to detect the filter coefficient corresponding to the provided timbre selector key signal, and changes the filter coefficient of the 14-tap FIR filter  213  to the detected filter coefficient, and the filter  213  then filters the PCM data inputted into the 14-tap FIR filter  213  with the changed filter coefficient to thereby process the conversation. 
     Although not shown, upon detecting the end of a conversation after changing the filter coefficient of the 14-tap FIR filter  213 , the control unit  111  changes the filter coefficient of the 14-tap FIR filter  213  back to the same filter coefficient as the original voice processing filter coefficient. 
     As described hereinabove, the invention has the advantages of enabling a change and/or selection of the transmitted and/or received voice data timbres so that conversation voice timbres can be provided to satisfy the tastes of the cellular telephone terminal users. 
     While the invention has been described with reference to a detailed example of the preferred embodiment thereof, it is understood that variations and modifications thereof may be made without departing from the true spirit and scope of the invention. Therefore, it should be understood that the true spirit and the scope of the invention are not limited by the above embodiment, but defined by the appended claims and equivalents thereof.