User manual TEXAS INSTRUMENTS TAS5508C DATA MANUAL 09-2010

[. . . ] TAS5508C 8-Channel Digital Audio PWM Processor Data Manual PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Literature Number: SLES257 September 2010 TAS5508C SLES257 ­ SEPTEMBER 2010 www. ti. com Contents 1 2 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1. 1 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] Slopes k0, k1, and k2 define whether compression or expansion is to be performed within a given region, and the degree of compression or expansion to be applied. Slopes are programmed as 28-bit (5. 23 format) numbers. 2. 10. 1 DRC Implementation The three elements comprising the DRC include: (1) an rms estimator, (2) a compression/expansion coefficient computation engine, and (3) an attack/decay controller. · RMS estimator--This DRC element derives an estimate of the rms value of the audio data stream into the DRC. For the DRC block shared by Ch1 and Ch2, two estimates are computed--an estimate of the Ch1 audio data stream into the DRC, and an estimate of the Ch2 audio data stream into the DRC. The outputs of the two estimators are then compared, sample-by-sample, and the larger-valued sample is forwarded to the compression/expansion coefficient computation engine. Two programmable parameters, ae and (1 ­ ae), set the effective time window over which the rms estimate is made. For the DRC block shared by Ch1 and Ch2, the programmable parameters apply to both rms estimators. The time window over which the rms estimation is computed can be determined by: *1 t + window F n(1 * ae) S · Compression/expansion coefficient computation--This DRC element converts the output of the rms estimator to a logarithmic number, determines the region where the input resides, and then computes and outputs the appropriate coefficient to the attack/decay element. Seven programmable parameters, T1, T2, O1, O2, k0, k1, and k2, define the three compression/expansion regions implemented by this element. Attack/decay control--This DRC element controls the transition time of changes in the coefficient computed in the compression/expansion coefficient computation element. Four programmable parameters define the operation of this element. Parameters ad and (1 ­ ad) set the decay or release time constant to be used for volume boost (expansion). Parameters aa and (1 ­ aa) set the attack time constant to be used for volume cuts. The transition time constants can be determined by: *1 *1 ta + t+ d F n(1 * aa) F n(1 * ad) S S · 2. 10. 2 Compression/Expansion Coefficient Computation Engine Parameters There are seven programmable parameters assigned to each DRC block: two threshold parameters--T1 and T2, two offset parameters--O1 and O2, and three slope parameters--k0, k1, and k2. The threshold parameters establish the three regions of the DRC transfer curve, the offsets anchor the transfer curve by establishing known gain settings at the threshold levels, and the slope parameters define whether a given region is a compression or an expansion region The audio input stream into the DRC must pass through DRC-dedicated programmable input mixers. These mixers are provided to scale the 32-bit input into the DRC to account for the positioning of the audio data in the 48-bit DAP word and the net gain or attenuation in signal level between the SAP input and the DRC. The selection of threshold values must take the gain (attenuation) of these mixers into account. The DRC implementation examples that follow illustrate the effect these mixers have on establishing the threshold settings. T2 establishes the boundary between the high-volume region and the mid-volume region. T1 establishes the boundary between the mid-volume region and the low-volume region. Both thresholds are set in logarithmic space, and which region is active for any given rms estimator output sample is determined by the logarithmic value of the sample. 36 Description Submit Documentation Feedback Product Folder Link(s): TAS5508C Copyright © 2010, Texas Instruments Incorporated TAS5508C www. ti. com SLES257 ­ SEPTEMBER 2010 Threshold T2 serves as the fulcrum or pivot point in the DRC transfer function. O2 defines the boost (> 0 dB) or cut (< 0 dB) implemented by the DRC-derived gain coefficient for an rms input level of T2. [. . . ] All products are sold subject to TI's terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI's standard warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by government requirements, testing of all parameters of each product is not necessarily performed. [. . . ]