SLAS666B January 2010 – October 2018 TLV320DAC3101
PRODUCTION DATA.
Typical music signals are characterized by crest factors, the ratio of peak signal power to average signal power, of 12 dB or more. To avoid audible distortions due to clipping of peak signals, the gain of the DAC channel must be adjusted so as not to cause hard clipping of peak signals. As a result, during nominal periods, the applied gain is low, causing the perception that the signal is not loud enough. To overcome this problem, dynamic range conpression (DRC) in the continuously monitors the output of the DAC digital volume control to detect its power level relative to 0 dBFS. When the power level is low, DRC increases the input signal gain to make it sound louder. At the same time, if a peaking signal is detected, it autonomously reduces the applied gain to avoid hard clipping. This results in sounds more pleasing to the ear as well as sounding louder during nominal periods.
The DRC functionality in the is implemented by a combination of processing blocks in the DAC channel as described in Section 6.3.10.1.2.
DRC can be disabled by writing to page 0 / register 68, bits D6–D5.
DRC typically works on the filtered version of the input signal. The input signals have no audio information at dc and extremely low frequencies; however, they can significantly influence the energy estimation function in the dynamic range compressor (the DRC). Also, most of the information about signal energy is concentrated in the low-frequency region of the input signal.
To estimate the energy of the input signal, the signal is first fed to the DRC high-pass filter and then to the DRC low-pass filter. These filters are implemented as first-order IIR filters given by
The coefficients for these filters are 16 bits wide in 2s-complement format and are user-programmable through register write as given in Table 6-20.
COEFFICIENT | LOCATION |
---|---|
HPF N0 | C71 page 9 / register 14 and page 9 / register 15 |
HPF N1 | C72 page 9 / registers 16 and page 9 / register 17 |
HPF D1 | C73 page 9 / registers 18 and page 9 / register 19 |
LPF N0 | C74 page 9 / registers 20 and page 9 / register 21 |
LPF N1 | C75 page 9 / registers 22 and page 9 / register 23 |
LPF D1 | C76 page 9 / registers 24 and page 9 / register 25 |
The default values of these coefficients implement a high-pass filter with a cutoff at 0.00166 × DAC_fS, and a low-pass filter with a cutoff at 0.00033 × DAC_fS.
The output of the DRC high-pass filter is fed to the processing block selected for the DAC channel. The absolute value of the DRC LPF filter is used for energy estimation within the DRC.
The gain in the DAC digital volume control is controlled by page 0 / register 65 and page 0 / register 66. When the DRC is enabled, the applied gain is a function of the digital volume control register setting and the output of the DRC.
The DRC parameters are described in sections that follow.