ROHM has developed two automotive audio processor LSI chips that it says can provide the same sound quality as home theater systems while reducing the shock noise generated when switching volume or tone.
The BD3484FS has a built-in loudness function and the BD3489FS integrates a six-channel external input/output terminal capable of connecting directly to a DSP. Both feature 0.007% distortion and 10.5 Vrms output noise voltage.
The parts feature different functions for level meter display and spectrum analyzer display outputs but were designed to be compatible with ROHM’s multichannel sound-processor LSI series in terms of pin placement and register maps.
Bass programs such as input selector, input gain and volume gain are shared in common with other sound processor LSI series, even when set functions are ranked or changed according to product destination, which makes them compatible with many other sound processor LSIs and CPU software.
A switching circuit automatically calculates the optimal number of gain switching steps from the input signal level and gain change value, resulting in a smoother envelope waveform, eliminating shock noise generated during switching when silent at 20 Hz low audio signal input, and at 2 Vrms high audio volume input.
Compared with software-switching methods that constantly send gain setting values to the sound processor LSI – accurately timed with the microcontroller – until gain conversion is completed, the switching circuit in the BD3484FS and BD3489FS reduces the load on the microcontroller. The circuit integrates register circuits that require changed values to be sent only once, after which optimum gain change processing is performed automatically, eliminating microcontroller load while simplifying software development.
The parts also include a built-in low-pass filter that reduces the number of external components required. A subwoofer connection is supported for a more realistic sound.