Pioneer ctf 615 schematic

Page 2

- DIONEENI

THE DOLBY NR SYSTEM

A cassette tape travels at one quarter of the Speed
of an open-reel (19cm/sec, 4-track) tape, and its
track width is only 60 percent in comparison. The
cassette tape is thus clearly at a disadvantage with
respect to the signal-to-noise ratio.

The Dolby NR system is_designed to reduce the
noise called hiss which is inherent in tapes, and it is
effective in upgrading the signal-to-noise ratio. It is
so effective, in fact, that it is now indispensable to
cassette decks.

The basic principle of the Dolby NR system is as
follows: when signals with a relatively low level are
recorded, the Dolby NR circuitry enhances the
signals in the high-frequency range which has most
of the hiss components, and these signals are then
recorded. When they are played back, the circuitry
attenuates only those components which were
enhanced during recording. This returns the signal
components to the normal level, and the hiss is
reduced (by a maximum of 10dB) during playback
only for that level which was attenuated. When the
signal is relatively high level, the S/N ratio is
sufficient and so the operation of the Dolby NR

Normal recording, playback

Recording using the Dolby NR system

system is not necessary. The Dolby NR system
operates automatically in accordance with the
signal level, as shown in the figure Furthermore, if
the Dolby NR system is used for recording, the
recording level can be set relatively low which
enables almost distortion~free good sound quality
tape recordings.

Operating precautions

O The adjustment of the recording level is basically
the same as when the Dolby NR system is not
used.

c In order to make the most of the effect of the
Dolby NR system, choose a program source with
as little noise as possible.

0 If you have used the Dolby NR system to record
a program, make sure that you use it when
playing the same program back.

0 Playing back a normally recorded tape with the
Dolby NR system and playing back normally a
tape which was recorded by the Dolby NR
system will result in an unnatural reproduction
of the sound on the tape.

Playback using the Dolby NR system

High 3 high , High -
s 2 5 -~\___ -
E Medium 79 Medium g Medium t
5 1 3 ______
.i .- c
3 : -\_-
1 Low level components ?
are enhanced High
I Medium
Low

-> Frequency (Hz)

-> Frequency (Hz)

-> Frequency (Hz)

Low level components
which were enhanced
during recording are re-
turned to their original
form.