CD player components: Processors, Buffers …Oversampling using a DSPSlide 3Slide 4Output FilteringOutput FilteringBuffer memoryThe ability to read different formatsReferencesCD player components: Processors, Buffers …Walid El jebbariOversampling 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 samplesOversampling using a DSP•iOversampling using a DSP•iOutput 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)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 bandBuffer 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 bearingsThe 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