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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] · Thresholds T1 and T2 define, in dB, the boundaries of the three regions of the DRC, as referenced to the rms value of the data into the DRC. Zero-valued threshold settings reference the maximum-valued rms input into the DRC and negative-valued thresholds reference all other rms input levels. Positive-valued thresholds have no physical meaning and are not allowed. Although the DRC input is limited to 32-bit words, the DRC itself operates using the 48-bit word format of the DAP. The 32-bit samples input into the DRC are placed in the upper 32 bits of this 48-bit word space. This means that the threshold settings must be programmed as 48-bit (25. 23 format) numbers. CAUTION Zero-valued and positive-valued threshold settings are not allowed and cause unpredictable behavior if used. Copyright © 2010, Texas Instruments Incorporated Description Submit Documentation Feedback Product Folder Link(s): TAS5508C 35 TAS5508C SLES257 ­ SEPTEMBER 2010 www. ti. com · · Offsets O1 and O2 define, in dB, the attenuation (cut) or gain (boost) applied by the DRC-derived gain coefficient at the threshold points T1 and T2, respectively. Positive offsets are defined as cuts, and thus boost or gain selections are negative numbers. 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. 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. [. . . ] Falls within JEDEC MS-026 POST OFFICE BOX 655303 · DALLAS, TEXAS 75265 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI's terms and conditions of sale supplied at the time of order acknowledgment. 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