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1999 Apr 14 17
Philips Semiconductors Product specification
Audio processor with head amplifier for VHS hi-fi TDA9605H
6.9 Audio dubbing
The TDA9605H includes unparalleled functionality
supporting the audio dubbing function of hi-fi video
recorders. Audio dubbing is a feature which enables the
recording of new sound material on the linear audio track
(i.e. normal sound) of an existing recording. The dub-mix
mode is selected by setting bit IS2 = 1, bit IS1 = 0 and
bit IS0 = 1. Audio dubbing can be used in two different
ways:
• Output mix
• Input mix.
6.9.1 O
UTPUT MIX
A new additional recording is made on the linear audio
track. In the playback mode, the new linear audio sound
and the original hi-fi sound are combined. In this way the
hi-fi stereo quality remains and the linear audio sound is
partly used (e.g. for commentary only). However, there is
no control over the original hi-fi sound.
Mixing of the hi-fi and normal sound signals in the playback
mode is supported by the output select function mix-left,
mix-right and mix-stereo (bits OSN, OSR and OSL) and
creates a new fixed output signal of
1
⁄
2
× hi-fi plus
1
⁄
2
× normal.
6.9.2 I
NPUT MIX
A new complete recording is made on the linear audio
track (see Fig.4). In the playback mode, only the linear
audio sound is used. In this way the hi-fi stereo quality is
lost, but total freedom in defining the new sound material
is an extra advantage. Furthermore, such recording is no
longer restricted to playback on hi-fi video recorders (with
an output mix option).
The circuit changes into a mixing desk when using the
dub-mix mode of the input select function in combination
with the volume setting of normal select. A new linear
audio recording can be created by mixing together the new
and the original sound.
Continuous user control over amplitude and ratio mix of
the auxiliary input signal (e.g. a microphone input) and the
original hi-fi playback sound is possible using the left and
right channel volume controls. This function is realized
inside the IC by connecting the auxiliary input signal pair
(pins AUXL and AUXR) to the left channel volume control
and the hi-fi output signal pair to the right channel volume
control.
The settings of the output select function are used to
arrange the hi-fi selection and the output signals in the
dub-mix mode. However, some of these settings are
overruled in the dub-mix mode. The normal signal is
available on the line outputs for monitoring the dub-mix
recording signals in the output select function modes
mix-left, mix-right and mix-stereo.
Mix-stereo of the output select function is generally used
for audio dubbing. In combination with the volume setting
of normal select, user control over amplitude and ratio is
offered for the auxiliary and the hi-fi signal as follows:
(
1
⁄
4
× aux left +
1
⁄
4
× aux right) × volume left plus
(
1
⁄
4
× hi-fi left +
1
⁄
4
× hi-fi right) × volume right.
The dub-mix mode is to be used in the (hi-fi) playback
mode. In the record mode, a signal loop from output to
input can be closed which may cause audio oscillation.
The auto-normal switching is not active during the dub-mix
mode. The hi-fi sound is muted when no hi-fi input signal
is detected; bit AUTN is not affected.
Table 5 Dub-mix mode
OUTPUT SELECT
MODE
DUB-MIX OUTPUT
SELECTION
DUB-MIX INPUT
LEFT CHANNEL RIGHT CHANNEL
mute mute aux stereo mute
hi-fi left hi-fi left aux stereo hi-fi left
hi-fi right hi-fi right aux stereo hi-fi right
hi-fi stereo hi-fi stereo aux stereo hi-fi stereo
normal normal aux stereo mute
mix-left normal aux stereo hi-fi left
mix-right normal aux stereo hi-fi right
mix-stereo normal aux stereo hi-fi stereo