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SAA7824 Datasheet(PDF) 19 Page - NXP Semiconductors |
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SAA7824 Datasheet(HTML) 19 Page - NXP Semiconductors |
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19 / 89 page  2003 Oct 01 19 Philips Semiconductors Product specification CD audio decoder, digital servo and filterless DAC with integrated pre-amp and laser control SAA7824 7.9 Audio functions 7.9.1 DE-EMPHASIS AND PHASE LINEARITY When pre-emphasis is detected in the Q-channel subcode, the digital filter automatically includes a de-emphasis filter section. When de-emphasis is not required, a phase compensation filter section controls the phase of the digital oversampling filter to ≤±1° within the band 0 to 16 kHz. With de-emphasis the filter is not phase linear. If the de-emphasis signal is set to be available at pin V5, selected via decoder register D, then the de-emphasis filter is bypassed. 7.9.2 DIGITAL OVERSAMPLING FILTER For optimizing performance with an external DAC, the SAA7824 contains a 2 to 4 times oversampling IIR filter. The filter specification of the 4 times oversampling filter is given in Table 5. These attenuations do not include the sample-and-hold at the external DAC output or the DAC post filter. When using the oversampling filter, the output level is scaled −0.5 dB down to avoid overflow on full-scale sine wave inputs (0 to 20 kHz). Table 5 Filter specification 7.9.3 CONCEALMENT A 1-sample linear interpolator becomes active if a single sample is flagged as erroneous but cannot be corrected. The erroneous sample is replaced by a level midway between the preceding and following samples. Left and right channels have independent interpolators. If more than one consecutive non-correctable sample is found, the last good sample is held. A 1-sample linear interpolation is then performed before the next good sample; see Fig.13. In CD-ROM modes (i.e. the external DAC interface is selected to be in a CD-ROM format) concealment is not executed. 7.9.4 MUTE, FULL-SCALE, ATTENUATION AND FADE A digital level controller is present on the SAA7824 which performs the functions of soft mute, full-scale, attenuation and fade; these are selected via decoder register 0: • Mute: signal reduced to 0 in a maximum of 128 steps; 3/n ms • Attenuation: signal scaled by −12 dB • Full-scale: ramp signal back to 0 dB level; from mute it takes 3/n ms • Fade: activates a 128 stage counter which allows the signal to be scaled up or down in 0.07 dB steps – 128 = full-scale – 120 = −0.5 dB (i.e. full-scale if oversampling filter is used) –32 = −12 dB – 0 = mute. 7.9.5 PEAK DETECTOR The peak detector measures the highest audio level (absolute value) on positive peaks for left and right channels. The 8 most significant bits are output in the Q-channel data in place of the CRC bits. Bits 81 to 88 contain the left peak value (bit 88 = MSB) and bits 89 to 96 contain the right peak value (bit 96 = MSB). The values are reset after reading Q-channel data via pin SDA. PASS BAND STOP BAND ATTENUATION 0 to 9 kHz −≤0.001 dB 19 to 20 kHz −≤0.03 dB − 24 kHz ≥25 dB − 24 to 27 kHz ≥38 dB − 27 to 35 kHz ≥40 dB − 35 to 64 kHz ≥50 dB − 64 to 68 kHz ≥31 dB − 68 kHz ≥35 dB − 69 to 88 kHz ≥40 dB |
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