AN332
Rev. 0.8
315
AM Properties
The properties and commands in this section are related to AM mode.
AM Mode Configuration (0x310x Properties)
AM_MODE_AVC_MAX_GAIN (0x3103) = 0x1543 (-C40, -D60)
AM_MODE_AFC_SW_PULL_IN_RANGE (0x3104) = 8695 (-C40, -D60)
AM_MODE_AFC_SW_LOCK_IN_RANGE (0x3105) = 11765 (-C40, -D60)
AM_MODE_AVC_MAX_GAIN is available in -C40 and -D60 devices with a default max gain of 16 dB. In -B20, the
AVC gain is set at maximum and not available through a property. To make -C40 or -D60 behave as -B20, set
AM_MODE_MAX_GAIN to 0x7800.
AM shortwave AFC range properties are available in -C40 and -D60 devices (supported by Si4734/35 devices
only). The default values of these properties provide similar behavior to the behavior of -B20 devices. However, in
-B20 devices, these properties are not available through the programming API.
AM Soft Mute Configuration (0x330x Properties)
AM_SOFT_MUTE_SLOPE (0x3301) = 2 (-B20), 1 (-C40, -D60)
AM_SOFT_MUTE_MAX_ATTENUATION (0x3302) = 16 (-B20), 8 (-C40, -D60)
AM_SOFT_MUTE_SNR_THRESHOLD (0x3303) = 10 (-B20), 8 (-C40, -D60)
Settings for Audio Soft Mute
Soft mute is active when SNR falls below the given AM_SOFT_MUTE_SNR_THRESHOLD. When active, the
output audio will be decreased at a set rate until the target soft mute attenuation is achieved. In -B20 devices the
threshold is 10 dB, whereas in -C40 and -D60 devices it is 8 dB.
The target soft mute target attenuation - up to a set maximum attenuation level - is calculated as the difference
between the soft mute threshold and the received SNR multiplied by a scalar value called the soft mute slope. The
default value of this property is 1 dB/dB in -C40 and -D60. In -B20, the value used is 2 dB/dB.
The maximum soft mute attenuation level is 10 dB in -B20. In -C40 and -D60 devices, the maximum level can be
set by a property AM_SOFT_MUTE_MAXIMUM_ATTENUATION, which has a default value of 8 dB.
The soft mute default changes in -C40 and -D60 have been made to improve weak signal listening experience.
