What is Yamaha CINEMA DSP
Have you ever heard about Yamaha Cinema DSP? This is an enhancement processor
for home theater purposes designed by Yamaha, the inventor of today's Home
Theater possibilities. This page will give you an idea of Cinema DSP as
well as basic technologic knowledges about DSP.
Yamaha and Home Theater are not only linked together
by amplifiers and AV products. Home Theater is born with Yamaha audio products
in the early 80s. Indeed Yamaha was of the first to introduce home theater on the world wide
audio market the technologies developed by the Dolby Laboratories for Movie soundtracks.
Yamaha engineers were the firsts to create integrated Dolby surround circuits for
home cinema purposes and they also were in the firsts to design Dolby Pro-Logic chips
using digital signal processing algorithm in small LSIcs (Large scale Integrated Circuits).
YAMAHA AND HOME THEATER
Furthermore, Yamaha products are elaborated in very different conditions
than other AV products. Yamaha is the world's largest maker of musical instruments
using digital techniques, they also design concert halls all over the world.
As a result Yamaha's broad background in all these areas has played an important role
in the design of DSP technologies applied to Home Entertainment. They do really know
how to measure and reproduce with high quality sound the acoustic soundfields
of actual places such as jazz clubs or concert halls.
Yamaha rendering sound systems have nothing to see
with "DSP processors" of any other customers. The soundfield created is much
more complex and the results are by far much more realistic. Even THX with its
enhancements may not reach the level of space and liveness of Cinema DSP concerning
the simulation of movie theater sounfields.
Cinema DSP was born in 1986 and was really achieved in
1988 after Dolby Pro-Logic was released. However Dolby Pro-Logic surround
channel provides a poor and weak "spot" of sound since this channel is mono.
Therefore you only get a small surround soundfield, actually nothing to see
with large movie theaters where many speakers are used at the surround channel.
As a result yamaha engineers achieved some enhancements by using A DSP in
series with the Dolby Pro-Logic decoder, that is cinema DSP, to create the
type of spacious surround heard in the movie theaters. This is a seven or
five speakers based system with all digital processing. All channels are
stereo but this is not discrete stereo , which means that all signals remain
WHAT IS CINEMA DSP ?
A Typical Yamaha
you may find on Cinema DSP are either video modes (movie theater 35 and 70mm
are the bests) and HiFi modes (church, Concert Halls, Jazz club sound very natural).
But Cinema DSP also means many features and facilities
linked to general AV operations.
You may wonder the effectiveness of such simulations. Cinema DSP however has nothing to see
with usual Dolby ProLogic process, AC-3 or THX enhancements:
Dolby Pro Logic is the means to hear in true conditions the mix
designed by sound engineers during the process of the movie soundtrack.
Consequently this is a matter of taste to know if you need it or not. Please note
that Cinema DSP does not add further effetcs to the original soundtrack. The two front effects added
are correlated with other channels and only provide efficient soundfields. Basically Cinema DSP
is a 4 channel system, but the enhancements give rise to a really improved sound diffusion and
makes you feel as if you were seating in a movie theater or a church.
THX is a quality label designed for home theater purposes in order
to improve the sounding quality level of Dolby Pro Logic. This is a means to adapt soundtracks
to home entertainment.
Cinema Yamaha DSP makes you hear the movie as you would hear it
in a movie theater with corresponding spaciousness and sounding characteristics.
AC-3 is fully discrete 5.1 channel system giving
you the possibility to hear the digital mix of the latest movie soundtracks.
Cinema DSP processing is achieved thanks to very small LSICs
(large scale integrated circuits) developed by the Yamaha
research laboratories using current digital signal processing technologies. This chip shown in the picture
on the right gathers both Dolby decoding circuit and the DSP. This prevents electric or magnetic
fields from distorting the digital informations running at very high speed in the processor.
The DSP is like a computer processor but devoted to audio applications. The main difference
with computer processors is that they are specially designed for 16 bits comparison and
multiplication and multiplication-accumulation in terms of signal processing requirements.
Input sound is converted into digital samples that are treated following an algorythm
contained in memory (ROM). Resulting data for each channel are stored into RAM in order
to process the next sample. Then all channels are converted back into analog signals.
HOW DOES CINEMA DSP WORK ?
You need to understand what is a soundfield to realize the Yamaha Cinema
DSP process. Basically a soundfield is a mix of sounds generated by a places having typical
reflections or sounding capacities. Usually the parameters describing the origins of a
soundfield depends upon frequency. The resulting soundfield
in a room depends on characteristics such as geometry, wall texture,... If a signal is
emitted in the room you'll hear a soundfield depending on all these parameters but initialy
all the soundfield was created by the single signal you generated. This is known as
signal correlation. If you change the frequency of the original signal, the soundfield will be different
since resonnance effects may occur at this frequency. If you want to recreate the soundfield of a place,
you need to make very precise measures of the reverberations, reflections or resonnances for all the
audio frequency range (20Hz-20kHz) with corresponding amplitudes and time delays or time required for
a signal to decay below a stated level. For example a jazz club raises direct sounds with high early
first reflections and poor reverberations rate. On the other hand, a concert hall will have
very little direct sounds but plenty of long time decaying reverberations and long first
reflections. All this work is then converted into software instructions
that will be used by the DSP to process the soundfield using input signal. Consequently the process
of an AUDIO DSP now appears to be quite obvious to understand :
The two input signals are converted by sampling and quantization
into digital data. Converters are usually 16 to 20 bits resolution (the higher the better) at
44.1kHz or twice the audio bandwidth according to the Nyquist Cryterion.
Samples are stored into RAM. They are not processed firstly
since next samples are required. They will be used after a few clock cycles by the DSP.
The DSP compares previous samples to older ones and
current ones. The results are analysed using software stores in ROM. This stage is very important
since comparison between samples allows correlation index to be found and gives all the
frequencies comprised in the little part of signal being processed.
Using the results of the signal analysis the DSP processes
the output data to be sent to the different output signals. A new correlation and a
frequency based process are applied as well as amplitude control
following the specifications of the soundfield to simulate (software). A set of errors is
implemented to avoid distortion in the signal or processing errors.
The DSP may store samples in another RAM for a few hundreeds
of clock cycles in order to generate the desired delay times. Reverberation is achieved by
sending the same data many times with a decaying intensity on the channel where it occurs
and by sending a corresponding amount of the same signal to other channels to simulate
the spaciousness of the reverberation.
All output signals are finally converted into analog form
and are rearranged by analog processing to provide fully musical signals.
Many different soundfields may be processed with the Yamaha Cinema
DSP chip (usually about 10 to 20 of them are available on amplifiers) but they are all
based on the parameters to simplify the process and make it running faster
(delay time, amount of reverberations, amplitude of the different channels and spaciousness
are controlable). The speed of the processor is of a few megahertz. The figure below
describes the main digital features surrounding the DSP.
The final results provided by Cinema DSP are the following. The DSP
adds two more effect channels on the front by processing the correlation between center
and main pro logic channels. The spaciousness is emphasized by sending part of the rear channel
to these front effects with required decaying reverberations and frequency response. The rear channel
is stereo in terms of sounfield. Both rear channels are independantly amplified and it is a
simulated stereo effect but they remain correlated all the same. What I mean by simulated stereo is a complex
mixture of correlated sounds actually exactly like those created with mono recordings in studios and that you
find on all your CD (except live recordings and classical recordings using stereophonics microphones).
Front effect channels are stereo as well and the top range amplifier provides
stereo subwoofer outputs (DSPA-2070). All the parameters are controlables and settings may be stored.
Cinema DSP is not only a few more effects and 7 channels processing.
It also provides some very convenient facilities developed for general AV environment. These are mainly:
CINEMA DSP FACILITIES
Very useful On Screen Display with DSP parameters control, test signals, center modes,...
Center speaker 5 frequency bands for adjustments so that tonal
character of center matches that of the main stereo pair.
DSP Parameters control and storage (channel level, delay time, liveness, room size)
Full functions on remote control (programmable for the DSPA-970 and DSPA-2070)
Pre outputs for main, center, effects and sub on many models
Front mix switch for seven or five speakers configurations
Input level trim to give all your sources the same input level (very useful)
Last updated Feb.1996
CINEMA DSP is a trademark of Yamaha