DPL4519G Просмотр технического описания (PDF) - Micronas

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DPL4519G

Sound Processor for Digital and Analog Surround Systems

Micronas 

PRELIMINARY DATA SHEET

DPL 4519G

2.6.3. Application Tips for using 3D-PANORAMA

2.6.3.1. Sweet Spot

Good results are only obtained in a rather close area

along the middle axis between the two loudspeakers:

the sweet spot. Moving away from this position

degrades the effect.

2.6.3.2. Clipping

For the test at Dolby Labs, it is very important to have

no clipping effects even with worst case signals. The

I2S-prescale register has to be set to values of max

10hex (16dec). This is sufficient in terms of clipping.

However, it was found, that by reducing the prescale to

a value lower than 16dec more convincing effects are

generated in case of very high dynamic signals. A

value of 10dec is a good compromise between overall

volume and additional headroom.

Test signals: sine sweep with 0 dBFS; L only, R only,

L&R equal phase, L&R anti phase.

Listening tests: Dolby Trailers (train trailer, city trailer,

canyon trailer...)

2.6.3.3. Loudspeaker Requirements

The loudspeakers used and their positioning inside the

TV set will greatly influence the performance of the vir-

tualizer. The algorithm works with the direct sound

path. Reflected sound waves reduce the effect. So it’s

most important to have as much direct sound as possi-

ble, compared to indirect sound.

To obtain the approval for a TV set, Dolby Laboratories

require mounting the loudspeakers at the front of the

set. Loudspeakers radiating to the side of the TV set

will not produce convincing effects. Good directionality

of the loudspeakers towards the listener is optimal.

The virtualizer was specially developed for implemen-

tation in TV sets. Even for rather small stereo TV's, suf-

ficient sound effects can be obtained. For small sets,

the loudspeaker placement should be to the side of the

CRT; for large screen sets (or 16:9 sets), mounting the

loudspeakers below the CRT is acceptable (large sep-

aration is preferred, low frequency speakers should be

outmost to avoid cancellation effects). Using external

loudspeakers with a large stereo base will not create

optimal effects.

The loudspeakers should be able to reproduce a wide

frequency range. The most important frequency range

starts from 160 Hz and ranges up to 5 kHz.

Great care has to be taken with systems that use one

common subwoofer: A single loudspeaker cannot

reproduce virtual sound locations. The crossover fre-

quency must be lower than 120 Hz.

2.6.3.4. Cabinet Requirements

During listening tests at Dolby Laboratories, no reso-

nances in the cabinet should occur.

Good material to check for resonances are the Dolby

Trailers or other dynamic sound tracks.

2.6.4. Input and Output Levels for

Dolby Surround Pro Logic

The nominal input level (input sensitivity) for the I2S-

Inputs is −15 dBFS. The highest possible input level of

0 dBFS is accepted without internal overflow. The I2S-

prescale value should be set to values of max 0 dB

(16dec).

With higher prescale values lower input sensitivities

can be accommodated. A higher input sensitivity is not

possible, because at least 15 dB headroom is required

for every input according to the Dolby specifications.

A full-scale left only input (0 dBFS) will produce a full-

scale left only output (at 0 dB volume). The typical out-

put level is 1.37 Vrms for DACM_L. The same holds

true for right only signals (1.37 Vrms for DACM_R). A

full-scale input level on both inputs (Lin=Rin=0 dBFS)

will give a center only output with maximum level. A

full-scale input level on both inputs (but Lin and Rin

with inverted phases) will give a surround-only signal

with maximum level.

For reproducing Dolby Pro Logic according to its spec-

ifications, the center and surround outputs must be

amplified by 3 dB with respect to the L and R output

signals. This can be done in two ways:

1. By implementing 3 dB more amplification for center

and surround loudspeaker outputs.

2. By always selecting volume for L and R 3 dB lower

than center and surround. Method 1 is preferable,

as method 2 lowers the achievable SNR for left and

right signals by 3 dB.

2.7. SCART Signal Routing

2.7.1. SCART Out Select

The SCART Output Select block includes full matrix

switching facilities. The switches are controlled by the

ACB user register (see page page 30).

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