From: hsu@acuson.com (William Hsu)
Subject: Re: Yamaha E1000 vs Sony TA-E2000ESD
Organization: Acuson; Mountain View, California
Date: Wed, 27 Jan 1993 01:20:54 GMT

michael@Canada.lsil.com (Michael Smith) writes:

>>4) Are the two extra channels in Yam worth it ? Are they missing on the Sony ?

>The two extra channels on the E1000, I believe, are just duplicates of the rear
>channels.  Note that I haven't verified this!  The Dolby Pro-Logic specification
>only defines four channels:

>	Left Main
>	Right Main
>	Center
>	Rear

>Although there are two rear speakers, they are mono.  The E1000 can mix the
>two front effect channels into your front speakers.  I haven't heard much of a
>difference with this option compared with all 7 speakers.


From what I could deduce from the Yamaha literatures, my understanding of
how the "effects" channels work differs with the above statement.

While it's true that Dolby ProLogic only specifies four channels described
above, the E1000/A1000 also does additional DSP processing from the output
of the ProLogic decoder to "simulate" a specific sound-field environment.
This is true for the modes 35mm Theatre (Dolby ProLogic Enhanced), 70mm
General Theatre (Movie Theatre General), and 70mm Adventure Theatre (Movie
Theatre Adventure).  The regular Dolby ProLogic mode does no additional DSP
processing.

Now for the four other video modes (Rock Concert Video, Classical/Opera
Concert Video, TV Drama, and TV Variety/Sports), a "directional-enhancement"
circuitry is used to incorporate the use of center channel (much like Dolby
ProLogic), but it does not follow Dolby ProLogic specs.  And the output of
that is fed to the DSP for sound-field simulation.

The 16 music modes bypasses the Dolby Prologic/directional-enhancement
circuitry (because it doesn't use the center channel) and only uses the DSP
chip.

The output of the DSP is front mains, center (where appropiate), front
effects, and rear effects.  The front mains and center are unaltered as far
as the DSP chip is concerned.  So the DSP generates sound-field information
based on its inputs and puts them out on the "effects" channels.  Now for a
5-channel setup, there is the option of mixing front effects channel with
front mains so you only have two main speakers in the front.  The other
option is to use a 7-channel setup where the front main gets unprocessed
signals and the effects speakers produces effects only.

If you imagine what Yamaha had to go through in order to obtain the
sound-field parameters for the DSP chip, it would make sense that front
effects channels are NOT the same as the rear effects channels.  Yamaha
claims that they did thousands of on-site measurements (w/ a
omni-directional microphone) to obtain sound-field parameters.  Surely the
signals coming from the back side of a concert hall is DIFFERENT from the
signals coming thru the front.

As to whether the effects channels are mono or stereo, that I don't know.
I tried to play a single-freq test signal that outputs only to one channel,
and I listened to the rear effects speakers.  Both speakers generated a
"processed" version of that signal, but I'm not sure if the output levels
were the same.  From that experiment, I concluded that the effects are mono.
After pondering about this question a little more, it kind of makes sense.
If Yamaha took their measurement in a (left-to-right) symmetrical listening
environment, and the test output is a point (mono) source, then all the 
reverb and ambiance signals coming off the symmetrical environment would 
have equal L+R levels.  Please correct me if you think this is not the case.

William
-- 
/-----------------------------------------------------------------------------\
| William Hsu				If it is bug-free, then I haven't     |
| Acuson, Test Engineering		got the chance to test it yet	      |
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