| 摘要 |
An apparatus and method for combining a multiple-bit digital audio signal with a single bit audio signal is provided. A host computer receives a single-bit audio signal from one or more PCMCIA cards plugged into the host computer. The single-bit audio signal may be a simple beep, or may be a pulse width modulated (PWM) signal that encodes more sophisticated audio. The program audio generated in response to software executing on the host computer is typically encoded in a multiple-bit pulse code modulated (PCM) audio signal. The apparatus upsamples the multiple-bit PCM audio signal generated by circuitry on the host computer to produce a first upsampled PCM signal. The apparatus converts the PWM signal from the PCMCIA card(s) to produce a second upsampled PCM signal. The first and second upsampled PCM signals are merged in an interpolation circuit to produce a composite digital signal that encodes both the program audio and the sound carried on the PWM signal. The composite digital signal is convened to an analog signal, preferably using delta sigma modulation techniques. The analog signal is used to drive the speaker of the host computer.
|
