Download CD player components: Processors, Buffers …

CD player components:
Processors, Buffers …
Walid El jebbari
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
Oversampling using a DSP
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Oversampling using a DSP
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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)
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
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
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
References
• www.tc.umn.edu/~erick205/Papers/paper.html
• www.answerbag.com/c_view.php/2012
• www.bestbuy.ca/learnmore/AskTheExpert/en/portabl
e_cd_players_faqs
• www.cdrfaq.org/