Cypress S6J3200 Series, Руководство пользователя

Страница: 500 / 1355

CHAPTER 20:Sound Mixer
S6J3200 Series Hardware Manual Document Number: 002-04852 Rev. *G 499
1.
Overview
This section gives a brief overview of the sound mixer.
Also refer to the chapter of "Sound System configuration" how to configure the sound mixer.
The sound mixer provides functions for mixing multiple input PCM (pulse code modulation) sound
sources.
Table 1-1
Feature Description
Input sound source 16-bit or 32-bit PCM sound source
Output sound source 32-bit PCM sound source
Number of input channels Up to 10 channels of sound source input are supported.
Number of output channels 1ch
Input sampling rate
Mixing of sound sources with different sampling rates is supported.
− WFG0 to 4 (five channels total): Input channels for fixed sampling rates: 48kHz
− PMIS0 to 4 (five channels total): Input channels for selectable sampling rates: 4, 8, 12, 24, 48, 96, and
44.1 kHz
Output sampling rate 48kHz
Mixing System Saturation calculation operation
FIR filter Prevention of sound quality change by sampling rate conversion
Volume effects
The volume and the mute, fade in, and fade out effects of the input sound source and output
sound source are controllable.
Notes:
−
The input sound source is input in 32-bit units, regardless of the sound source format. A monaural
sound source is input in 16-bit and 32-bit units.
−
16-bit monaural sound source output is not supported.
−
Sound waveform generator output may have a fixed connection to WFG0 to 4. It should be noted
that there may be specification limits on specific models.
−
The 44.1 kHz input sampling rate can be applied to only one of the input channels PMIS0 to 4.
Operation when 44.1 kHz is applied to multiple channels cannot be guaranteed from the
viewpoint of the mixing process load imposed by the sound mixer. It should be noted that there
may limits on specific models concerning the selection of other frequencies.
−
In the case of a sound source with a sampling rate that is not 48 kHz or 96 kHz, the sampling rate
is converted internally by the mixer to 48 kHz. Noise removal by an FIR noise filter is performed
before mixing to reduce change in sound quality due to distortion generated by this conversion.
However, noise removal by FIR filtering is not performed in the case of down sampling of a 96
kHz sound source to 48 kHz. Because of this, there is the risk of sound quality being affected by
aliasing generated at that time. The sampling rate must be determined with sufficient sound
quality evaluation being implemented by the system.
−
Mixed sound sources are calculated by the sound mixer's signed saturation calculation.
Saturation calculation uses a pre-defined minimum value or maximum value when a calculation
operation generates overflow. Mixing multiple high volume (large amplitude) sound sources
creates the risk of sound quality being affected by saturation calculation rounding error. Sound
mixing supports individual volume control for each channel, so adjustments can be made while
evaluating the result on the system.