Sony STR-DA9000ES - Fm Stereo/fm-am Receiver Technical Background - Page 11
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Digital amplifiers like the S-Master Pro design can be highly accurate—in
some respects they can even be too accurate. Phase linearity is an issue with
analog amplifiers and a contributor to analog sound. When you connect a real-
world amplifier to a real-world loudspeaker, the interaction causes significant
departure from phase linearity at frequencies below 30 or 50 Hz. Sony studies
show a typical deviation from linear phase of about +90 degrees. While not
making the bass any louder or softer, this shift does have a subtle effect, creating
warmer and more accessible bass.
The low-frequency phase response of the typical analog amplifier
departs from linearity at about 30 to 50 Hz. Because many audiophiles
are accustomed to seeing frequency plotted against amplitude in
decibels, this may look like a bass boost. It is not. It's a change in
phase, which is much more subtle.
Because this phase shift is common across many brands of amplifiers at
many price points, the shift has a broad effect on loudspeaker design.
Consciously or not, loudspeaker designers take this phase shift into account
when they fine-tune the sound of their products.
This raises an interesting dilemma. Should a new digital amplifier
incorporate this phase shift or leave the sound in its original state? After
extensive listening tests, Sony decided to give users the choice of applying an
equivalent phase shift in the digital domain, using a dedicated Digital Signal
Processor, the Sony CXD9776Q. This LSI adjusts low-frequency phase with
internal accuracy equal to a 65-bit process. We call this circuit the DC Phase
Linearizer, because it "restores" low-frequency phase, emulating the signal that
the speaker would get from a top-quality analog amplifier.
ES Receivers V3.0
DC Phase Linearizer
+90
Phase
0°
-90°
DC (0 Hz)
30~50 Hz
Frequency
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