Issue 133 August 2001
Listening Chips

Start • In The Realm Of The Sensory • Lip Reader • Walk The Talk • Soft Sounds • Yak Attack • Hearing Aid • Sources & PDF

WALK THE TALK

Actually, perhaps the title of this month’s article probably should be "Talking & Listening Chips" because the RSC-364 is equally adept at handling audio recording and playback including voice, music, and tone generation (for example, DTMF).

There are two choices for generating audio, each with its own trade-offs. An onboard 10-bit D/A converter is the logical candidate, but requires an external audio amplifier. By contrast, a PWM option can drive a small 32-W speaker directly.

Although called PWM, the latter is actually kind of a push-pull PCM (pulse count modulation). Two outputs are connected to the speaker terminals. When one is held low and the other is pulsed, the speaker will push. Reverse the pin functions and the speaker pulls. More pulses equals more amplitude (i.e., volume), with the speaker mechanical inertia acting as a low-pass filter. The frequency of reversing the pin functions (push versus pull) controls the pitch. Clever scheme, but the datasheet does caution you to be on the lookout for EMI generated by all the high-frequency square wave switching.

Besides recording your own audio for playback, Sensory makes it easy to import .WAV files with the Quick Synthesis tool as shown in Photo 2. For convenience, three compression options (uncompressed, 75% and 50%) are provided to allow you to choose the trade-off between sound quality and memory size.