Meridian America Meridian 518 ユーザーズマニュアル
Appendix 4
–Resolution Enhancement
52
518 User Guide
are boosted. This boost process is called pre-emphasis. Now, in the
channel, the energy is more evenly distributed with frequency, and any
high-frequency noise and distortion in the channel is further below the
signal. In other words we get a better distortion and noise result in the
channel.
channel, the energy is more evenly distributed with frequency, and any
high-frequency noise and distortion in the channel is further below the
signal. In other words we get a better distortion and noise result in the
channel.
Before playing back the signal, we need to de-emphasise it to bring the
overall frequency response back to where it should have been. By cutting
the high-frequencies back, we also reduce the noise and distortion
introduced in the channel.
overall frequency response back to where it should have been. By cutting
the high-frequencies back, we also reduce the noise and distortion
introduced in the channel.
This process is used everyday for FM broadcast, tape and cassette
recording, for LP (RIAA pre- and de-emphasis) and for some CDs.
recording, for LP (RIAA pre- and de-emphasis) and for some CDs.
Now, boosting high frequencies is possible only when the program does
not have too much high-frequency content. Obviously anything that has
been through a pre- and de-emphasis process has the required spectrum.
not have too much high-frequency content. Obviously anything that has
been through a pre- and de-emphasis process has the required spectrum.
The diagram below shows the pre-emphasis and de-emphasis curves for
CD – which are the curves used by 518. You can see that the highest
frequencies are boosted by nearly 10dB in the channel (on the disc).
CD – which are the curves used by 518. You can see that the highest
frequencies are boosted by nearly 10dB in the channel (on the disc).
Figure 4. Showing CD pre- and de-emphasis curves.
The 518 obtains resolution enhancement in making CD recordings by
using this pre-emphasis. All CD players know how to de-emphasise this
signal and recognise the pre-emphasis flag. When a signal coming in to
518 is pre-emphasised, the Emph light comes on. When 518 adds pre-
emphasis to a signal, the digital audio output stream carries an industry-
standard indication of pre-emphasis to tell downstream devices how to
handle this signal.
using this pre-emphasis. All CD players know how to de-emphasise this
signal and recognise the pre-emphasis flag. When a signal coming in to
518 is pre-emphasised, the Emph light comes on. When 518 adds pre-
emphasis to a signal, the digital audio output stream carries an industry-
standard indication of pre-emphasis to tell downstream devices how to
handle this signal.
The 518 obtains resolution enhancement in playback systems by boosting
the high-frequency signals as it travels through signal processing or the
digital filters and conversion parts of a DAC. In the above diagram
'Channel' can be the digital and conversion part of an outboard converter.
The last block, 'De-emphasis' is normally in the final analogue sections of
the converter.
the high-frequency signals as it travels through signal processing or the
digital filters and conversion parts of a DAC. In the above diagram
'Channel' can be the digital and conversion part of an outboard converter.
The last block, 'De-emphasis' is normally in the final analogue sections of
the converter.
Well-designed converters use analogue de-emphasis so that all the noise
of the digital filters and converter are reduced. There are some cheap
implementations around that use digital-de-emphasis. This is bad design
and the benefits of this type of resolution enhancement are reduced if
of the digital filters and converter are reduced. There are some cheap
implementations around that use digital-de-emphasis. This is bad design
and the benefits of this type of resolution enhancement are reduced if