Peak Extension (PE)

HDCD includes a function called peak extension. Peak extension is an optional function that applies a digitally

implemented soft limit (6 dB) to rare peaks in the music signal before recording on the disc. HDCD discs include ones to

which peak extension has been applied, and ones to which peak extension has not been applied. The LC78628E HDCD

decoder block automatically detects this optional peak extension processing and restores the attenuated peaks to their

original shape.

Gain Scaling (GS)

After decoding, recordings to which peak extension was applied have peaks that are 6 dB higher, and the D/A converter

must reproduce these peaks. Therefore, the D/A converter input block average level is reduced by 6 dB. This average

level must be matched to the average level when recordings made without peak extension or non-HDCD recordings are

played back. This average level adjustment is called gain scaling (GS).

The LC78628E allows applications to switch between performing this gain scaling digitally within the IC or externally

using analog circuits. The EXSCA flag in the HDCD control register is used for this setting. The GAIN pin is used as the

control signal if gain scaling is performed in the analog domain.

Low-Level Extension (LLE)

HDCD includes a function called low-level extension. This is a function that compares the average level of a song to a

threshold level and raises that average level (i.e., it compresses the low levels). This is an optional function, and there are

both HDCD recordings that are made with low-level extension, and ones in which it is not used. The LC78628E

automatically recognizes low-level extension discs and returns compressed low levels to their original values.

HDCD Signal Output — Pin 25: HDCD

If the disc being played back was HDCD encoded, the HDCD output pin outputs a high level. At all other times it outputs

a low level. This pin output can be used in end products to provide an LED indicator that indicates when an HDCD disc

is being played. The HDCD signal can also be read by the control microprocessor using the port input instruction.

Gain Signal Output — Pin 37: GAIN

The GAIN pin is used when gain scaling is performed in the analog domain. This pin must be left open if gain scaling is

performed in the digital domain.

When analog gain scaling is used, a high level is output from the GAIN pin to indicate that peak extension processing

had been applied to the disc being played back. A low level is output from the GAIN pin for HDCD discs that did not

have peak extension applied and for non-HDCD discs. For analog domain gain scaling, the application must include an

external circuit that, when the GAIN pin output level is high, increases the output level by 6 dB over the level when the

pin output level is low. The GAIN signal can also be read out using the port input instruction.

Digital Attenuator

The HDCD filter block includes a digital attenuator that allows the attenuation level to be set in 0.5 dB steps with

commands. After a reset, the attenuation level goes to fully muted (the –

∞ muted state with an attenuation code of $00).

This means that applications must set the attenuation code to $FF (the maximum setting value) to output the audio signal.

The attenuation code can be set to one of 256 values from $00 to $FF (0.5 dB steps) by applying commands from the

control microprocessor. The setting command is a 2-byte command. This command differs from the 2-byte command

used for track checking, and is the type where 16 bits of command data are transferred consecutively after setting RWC

high. There is no need to send the 2-byte command reset instruction ($FF) after using this command. (See the “Two-byte

commands (RWC set once)” section on page 13.)

No. 6329-25/40

LC78628E

EXSCA

Gain scaling type

RES = low

0

Digital gain scaling

q

q

1

Analog gain scaling