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  1. CD player components: Processors, Buffers … Walid El jebbari

  2. Oversampling using a DSP • Oversampling means using a sampling frequency greater than that dictated by the Nyquist theorem • It results in great performance gains; an increase in signal-to-noise ratio and a decrease in the quantization noise • Done using a digital signal processor (digital filter) which takes in audio samples, performs an operation on them, and then outputs audio samples. • Oversampling can be viewed as interleaving zeros between each sample with additional samples

  3. Oversampling using a DSP • i

  4. Oversampling using a DSP • i

  5. Output Filtering • The role of the output filters is to smooth out the waveform from the digital-to-analog converters • the output filter stage has witnessed a great deal of improvement since 1982 • Early 16-bit players used brickwall reconstruction filters • These filters had a very sharp cutoff characteristic and held the signal gain close to unity • The problem was that they had “big” phase nonlinearities at high frequencies, and high-frequency group delay (change in phase shift with respect to frequency)

  6. Output Filtering • current players have taken advantage of digital oversampling filters placed upstream of the DAC along with a gentle analog reconstruction filter • These filters have a gentler cutoff characteristic than the brickwall filters, because the oversampling filter shifts noise outside the audio band • Its design is noncritical and low-order--which guarantees excellent phase linearity • phase distortion can be held at ±0.5° over the entire audio band

  7. Buffer memory • CD players incorporate a buffer memory that “reads ahead” on the disc stores up to 45 seconds of audio as a CD plays • When the player is bumped or jostled, it interrupts the laser’s ability to read the data from a CD • The buffer memory temporarily reads the contents of the buffer so playback can continue uninterrupted while the laser assembly regains its bearings

  8. The ability to read different formats • CD-R was designed to be read by an infrared 780nm laser • DVD uses a visible red 635nm or 650nm laser, which aren't reflected sufficiently by the organic dye polymers used in CD-R media • As a result, many DVD players can't read CD-R media • Some DVD players come with two lasers so that they can read CD-R; one infrared for CDs, one visible for DVDs

  9. References • • • •