参数资料
型号: TAS3103DBTG4
厂商: TEXAS INSTRUMENTS INC
元件分类: 消费家电
英文描述: SPECIALTY CONSUMER CIRCUIT, PDSO38
封装: GREEN, PLASTIC, TSSOP-38
文件页数: 123/148页
文件大小: 1247K
代理商: TAS3103DBTG4
317
3.6
Soft Volume/Loudness Processing
Each of the three monaural channels in the TAS3103 has dedicated soft volume control and loudness compensation.
Volume level changes are issued by I2C bus commands in the I2C slave mode and by setting the appropriate GPIO
pin to logic 0 in the I2C master mode. Commanded changes in volume are implemented softly, using a smooth S-curve
trajectory to transition the volume to the newly commanded level.
Volume commands are formatted as signed 5.23 numbers. The maximum volume boost then is 24 dB
(4 bits x 6 dB/bit); the maximum volume cut is
∞ with a volume command of zero. The maximum finite volume cut
is 138 dB (23 bits x 6 dB/bit). The resolution of the volume adjustment is not fixed over all gain settings. For large gains
the resolution of the volume adjustment is very fine, and the resolution of the volume adjustment decreases as the
volume gain decreases. As an example, at maximum gain, the volume level can be adjusted to a resolution of
0.000001 dB [(138 + 24) dB adjustment range/227 adjustment steps]. At the other end of the gain scale, if the volume
setting is at the maximum finite cut (volume command = 0x0000001) and is increased by one count (volume command
= 0x0000002), a 6-dB adjustment is realized.
Each monaural channel volume control is also assigned a separate mute command, which has the same effect as
issuing a zero-valued volume command. If loudness is enabled, disabling it by setting the parameter G to zero is
necessary to obtain a total cut (
∞ dB). This requirement is further discussed in the paragraphs that follow.
Loudness compensation tracks the volume control setting to allow spectral compensation. An example of loudness
compensation would be a boost in bass frequencies to compensate for weak perceived bass at low volume levels.
Both linear and log control laws can be implemented for volume gain tracking, and a dedicated biquad filter can be
used to achieve spectral discernment.
3.6.1
Soft Volume
Figure 315 is a simplified block diagram of the implementation of soft volume and loudness compensation. A volume
level change (either via an I2C bus issued command in the I2C slave mode, or a GPIO-issued command in the I2C
master mode) initiates a transition process that assures a smooth transition to the newly commanded volume level
without producing artifacts such as pops, clicks, and zipper noise. The transition time, or volume slew rate, can be
selected to occupy a time window of either 2048 or 4096 audio sample periods. For 48-kHz audio, for example, this
equates to a transition time of 42.67 ms or 85.34 ms. It is anticipated that 42.67 ms is the transition time of choice
for most applications, and the 4096 sample transition option is primarily included to yield the same 42.67-ms transition
time for 96-kHz audio. The slope of the S-curve (and its implementation) is proprietary and cannot be altered.
If additional volume commands for a given monaural channel are received, while a previously commanded volume
change is still active, the last command received over-writes previous commands and is used. When the previously
commanded transition completes, the volume command last received while the transition was taking place is acted
upon and a new transition to this volume level initiated. For example, assume three volume commands are
sequentially issued, via the I2C bus, to adjust the volume levels of the three monaural channels in the TAS3103. The
first command received immediately triggers the start of a soft volume transition to the newly commanded level. The
other two volume commands are received and queued to await the completion of the currently active soft volume
transaction. When the first soft volume transition completes, and assuming no further volume commands have been
received to replace the other two volume commands received, the next two volume commands are activated, and
soft volume transitions on both monaural channels takes place. The total time then, for a 48-kHz audio sample rate
and a transition selection of 2048 FS cycles is 2 x 42.67 ms or 85.34 ms. If, during the first soft volume transition, a
second volume command is received for this same monaural channel, the second soft volume transition period would
have soft volume transitions taking place on all three monaural channels. It is also noted that the soft volume transition
time is independent of the magnitude of the adjustment. All volume commands take 2048 or 4096 FS cycles,
regardless of the magnitude of the change.
In the I2C slave mode, the status of a commanded soft volume transition can be found by reading bit 0 of the 32-bit
data word retrieved at subaddress 0xFF. If this bit is set to logic 1, one or more monaural channels are actively
transitioning their volume setting. If a volume transition is taking place on one of the monaural channels in the
TAS3103, volume commands received for the other two monaural channels are not acted upon until the active volume
transition completes. When the active volume transition does complete, the latest volume commands received for
the three monaural channels during the previous soft volume transition time are serviced.
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