● Channel divider units with high-speed DSP for fully digital signal processing● Standard configuration allows 4-channel (4-way) system setup ● 59
selectable cutoff frequency points ● Highly accurate 96 dB/oct attenuation slope● Time alignment function allows delay time setting in 0.5-cm steps ● Delay
compensator offsets signal delays in filter circuitry ● Further refined MDS++
D/A converter ● Output mode can be set to monophonic specifications

Multi-channel divider with fully digital signal processing – High-speed 40-bit floating
point DSP provides the processing power for four channel units supplied in standard
configuration. Highly accurate digital filters offer a choice of 59 cutoff frequency
points and up to 96 dB/octave attenuation. Integrated time alignment function
adjustable in 0.5-cm steps, and delay compensator for automatically offsetting any
filter circuit delays. Output mode can be changed to monophonic specifications.

❷ 2-way system for left and right 2-way monophonic setup
For left channel

Cutoff frequency

Cutoff frequency

Low range

High range

Low range

Channel B

Channel C

High range

For right channel

L
Preampliﬁer

R
DF-55

Channel A

MONO L

Channel D

MONO R

〔dBr〕
PASS

0
−10

6d

B/

6d

−20

12

ct

/o

18
dB
/o

/o
ct

24

ct

B/o
48d
ct

/oct

96dB/o96dB−80The divider units of one DF-55 are set to the "MONO
L" position, and the units of the other DF-55 to the"MONO R" position. This allows setting up a 2-way
to 4-way monophonic spec multi-amped system.

ct

−70

❸ 2-way to 4-way system, using two DF-55 units

/o

dB

dB

−60

ct

ct

/o

−50

/o
ct

dB

−40

oct

dB

ct

dB

12

−30

Two of the four divider units in the DF-55 are
set to the "MONO L" position and the othertwo units to the "MONO R" position. This
allows setting up a 2-way monophonic spec
system.

PASS

ct
B/o

B/o

The DF-55 features high-speed digital signal
processing with amazing power. Latest digital
circuit topology and advanced technology
come together in a filtering DSP that has a
32-bit mantissa and 8-bit exponent section.
The floating point principle enhances
calculation accuracy by dividing numericvalues into mantissa and exponent, thereby
preventing errors even when handling verysmall values. This results in dramatically
improved dynamic range and superiorprecision, allowing very steep cutoff slope
settings of 48 dB or 96 dB per octave.

The filter attenuation characteristics can be set to
6 dB, 12 dB, 18 dB, 24 dB, 48 dB, or 96 dB per
octave. The 96 dB/octave setting in particularallows the driver unit to reproduce only its
intended frequency without being affected byadjacent frequency bands. This makes it possible
to create a multi-amped system that takes
musical accuracy to an unprecedented level.

48d

implements fully digital signal processing

In this example, the left and right signals in the ultra-low
frequency range are mixed (channel A output mode is
set to "MONO L+R" position), for configuring athree-way system with a subwoofer.

per octave

24High-speed, high-precision DSP

Six filter slope characteristics up to 96 dB

18

Multi-amplification is regarded as the pinnacle of theaudio world. The term refers to dividing the musicalspectrum into several distinct bands and handlingeach of these using a dedicated power amplifier anddirectly connected speaker unit. Such a system isnecessarily more complex, but when configured andadjusted properly, it can achieve sound reproduction
on a scale that is not possible by any other means.
Sonic definition and sound quality can be optimizedby the user to obtain exactly the desired result.
Configuring a multi-amplified system affords truly
one of the greatest pleasures of audio.
The Digital Frequency Dividing Network DF-55
represents a full model change of the model DF-45.
A high-speed, high-precision DSP further minimizes
any calculation errors,
implementing accurate
filtering of the highest
order. Each bandwidthis handled by a
dedicated divider unit,
and a full array of
High-speed 40-bit floating point
Digital Signal Processor (DSP)
functions
includingfrequency dividing filters (low-pass, band-pass,high-pass) with 96 dB/octave attenuation, delay anddelay compensation, level control, and phaseswitching are implemented in the digital domain.
Digital as well as analog line and balanced inputs
are provided, and the unit comes as a 4-channel
device (for 4-way amplification) in its standard
configuration.

−90
−100

10

20

30

50

70 100

200

500

1k

2k

3k

5k

7k

10k

(Hz)

Frequency

Fig. 1 Divider Unit Slope Characteristics (Bandpass Filter)

Time alignment function allows delay[Cutoff frequency setting 100 Hz for lower and 1 kHz for upper range]

adjustment in 0.5-cm steps
Output mode of each divider unit can be set to

The sound emanating from a speaker travels through the
air at a speed of about 343.5 meters per second (whenthe ambient temperature is 20 degrees centigrade).
Compared to the propagation speed of light or of electricalsignals, this is extremely slow. When multiple speaker
units are used, necessarily located at different positions,
there will be differences in the time required for the soundto reach the ear of the listener. In a multi-speaker system,
each sound source position, namely the position of thediaphragm in the respective driver unit, is not aligned on
the front/back plane, also leading to different arrival timesof the sound. Compensating for such differences is calledtime alignment (see Figure 3). The DF-55 incorporates
a DELAY function that uses digital signal processing toelectrically adjust the time when the sound from eachdriver reaches the listener. Normally, a delay would be
expressed as a time value, but since the delay here iscaused by spatial distance, the DF-55 converts the delay
into a distance value (cm) for easier understanding.

STEREO , MONO L+R , MONO L , or MONO R

In normal use, the divider units will be set to
the STEREO position, but by changing thesetting to monophonic (MONO) operation, theleft-channel and right-channel DAC outputs
within the unit are added up, resulting in aparallel drive configuration that further
reduces residual noise.
❶ Use for a subwoofer (3D) system
Cutoff frequency

Ultra-low range (monophonic) Low range High range

In 3-way system,
channel D is set to
OFF

L
Preamplifier

R
DF-55

Channel A
MONO L＋R

Channel B

Channel C

STEREO

HS-Link

Channel A

HS-Link
ReceiverMDS＋＋
D/A Conversion System×4

DisplayLin
CoaxialDigitalInputs

DSP：Digital Signal Processor
CoaxialReceiver
Encoder

OpticalAssembly withhigh-speed DSP chip

Filter frequency points can be set over the range
from 31.5 Hz to 22.4 kHz in 1/6-octave intervals. In
addition, 10, 20, and 290 Hz points are also
provided, resulting in a total of 59 points. Each
divider unit is fully flexible and allows free selectionof the lower and upper cutoff frequency.

Floating Point

DAC

DSP

DAI
Decoder
Balanced

Date/ClockDistributor

Frequency

Level

Phase

Slope

Delay

Delay Comp

OutputAnalogInputsA/D
Converter

Hs-Link
DigitalOutputAnalogAttenuator
ON/OFF
BufferBalan

Hs-Link
TransceiverFig. 2 DF-55 Block Diagram

Mono
ON/OFFMDS＋＋
D/A Conversion System×4

Lin

Digital Filter

DAC

Line

BufferMaster Level
OpticalReceiver

A/D
Converter

59 selectable cutoff frequency points

MicroComputer

Digital Filter

Coefficient
MemoryBufferAnalogAttenuator
ON/OFF
BufferBalan

Channel B

Same as Channel A

Channel C

Same as Channel A

Channel D

Same as Channel A＜Time alignment using delay＞
d cm

t seconds
Delay function
H waveform
delays ○by t seconds

Delay
H

H

Delay

e TimeInput
L

L

Start time
L and ○
H sound source
Speaker unit ○(diaphragm) are d centimeters apart

L and ○
H signals
Delay ensures that ○arrive at the ear at the same time

Fig. 3 Time Alignment Principle

Speed of sound = 331.5 + 0.607 T [m/sec] T: temperature (°C)
Consequently, at 20°C, sound travels at about 343.5 m/sec.
H is set to d cm, theIn the example above, when DELAY function for ○H will be delayed by t = d/34,350 seconds, causing thesignal start for ○L and ○
H to reach the listener at the same time.
sound from ○MDS (Multiple Delta Sigma) is a revolutionary design which
employs several delta sigma type converters in a parallel
configuration. In the combined output of these multiple
converters, the ratio of conversion errors to the audio signal
becomes larger, resulting in a drastic improvement in all
relevant aspects of converter performance, such as accuracy,
S/N ratio, dynamic range, linearity, and THD. (When thenumber of converters is taken as "n", the improvement is n.)
Because the performance improvement afforded by the MDS
principle is not dependent on signal frequency or signal level,
noise at very low levels that
plagues the output of
conventional converters canalso be reliably reduced.
In the DF-55, four HyperstreamTM
DAC chips (ES9008 made by
ESS Technology) of the latest
generation are driven in parallel. Compared to a single
converter, this results in an overall performance improvement
by a factor of 2 (= 4). As shown in the diagram, the MDS++

circuit features an enhanced current-to-voltage (I/V) converter
for processing the D/A converter output current. A combinationof current summing and voltage summing is used, for optimized
operation.
The overall result is improved stability and top-notch
performance. The music emerges from a totally silent
background, with breathtaking detail resolution and accurate
spatial information.
(Normal phase output)

DAC 1

I (current)/V(voltage)
converter

I/V(Reverse phase output)

DAC 2

I/V

DAC 3

I/V

DAC 4

I/V

−
＋

Subtraction

Current summing

DAC output

Voltage summing

Block diagram of MDS++ converter

Other Functions and Features■ Digital attenuator with setting range from -40.0 dB to +12.0 dB (in 0.1-dB steps) allows
precise level adjustments for left and right channels.
■ "Analog ATT" function can be activated for specific channels to reduce residual noise whenusing high-efficiency midrange or high range speaker units (ON: -10 dB).
■ Versatile choice of input connectors. Digital signals can be supplied via coaxial, optical,and HS-Link inputs. Line and balanced inputs are available for analog signals.
■ "Full Level Output Protection" function safeguards the speakers if a digital signal
without volume control data is input (Output level reduction -40 dB).
■ Unused divider units can be set to OFF (all display elements and LED
indicators are out).
■ Safety Lock prevents inadvertently changing any settings.
■ Display indication can show predefined strings or custom strings
entered by the user (max. 8 characters, character set 97
characters).
■ Independent phase switching for left andright channel (4 patterns).

ne

Left
AnalogOutputs

nced

ne

nced

t seconds

High-performance HyperstreamTM DAC used for MDS++

Right
AnalogOutputs◆ The DF-55 comes standard with four units named CHANNEL A - D(4-way configuration). The assembly shown here carries the
coaxial digital input and output connectors, line/analog input
connectors, MDS++ D/A converter modules for
4 channels, and line/analog output
connectors.

Delay compensator function of DF-55 (providing automatic compensation for signal delays)
Besides delays caused by speaker placement,a certain delay will also occur when a signal
passes through a filter circuit. The DF-55
incorporates a function called "DELAY COMP"
that compensates for such delays. As an
example, the illustration at right shows a
simplified representation of how the delay
compensator function works in a 3-way system.
■ Regardless of whether a circuit is analog ordigital, when the signal has to pass through afilter, the output will be delayed by a certain
amount, causing a delay in step response
and impulse response.
■ Generally, a low-pass filter will have more
delay. The DF-55 therefore only provides
compensation when low-pass filtering is
used.
■ The lower the filter frequency and the steeper
the filter slope, the longer the delay.
ON

OFF＜Operation principle of delay compensator＞
DELAY COMP
〔Channel A〕
function
ON/OFFOFFb is delayed○

ON/OFF

Input

LOWER SLOPEUPPER SLOPELEFT LEVELRIGHT LEVELLEFT DELAY（cm）

RIGHT DELAY（cm）

DELAY COMPPHASEOUTPUTASSIGNMENT

t3−t2

OFF

b compensation time)t3−t2 (○

〔Channel B〕
ON
c is delayed by t3 seconds○

ON/OFFc
Output○〔When ON: Delayed by t3 seconds〕

t3

t3

Delay: 0 s

c compensation time)(○〔Channel C〕(High-pass filter)
As shown above, the signal
will be delayed by a different
durationwhen
passing
through different filter circuits.

When DELAY COMP is
ON, the time differenceabetween output signals ○,c is eliminated.
b and ○○,

When DELAY COMP is OFF, the output
signals in each channel will be shifted,
causing time misalignment. Output
signal vs input signal time lag (delay)

Actual delay compensatorindication is in cm, converted
from the above compensation
time value.

Cutoff frequency settings (Hz) (Cutoff characteristics: -3.0 dB, 59 points)
10
20 31.5 35.5
40
45
50
56
63
71
80
90
100 112 125 140 160 180 200 224 250 280 290 315
355 400 500 560 630 710 800 900 1000 1120 1250 1400
1600 1800 2000 2240 2500 2800 3150 3550 4000 5000 5600 6300
7100 8000 9000 10k 11.2k 12.5k 14k 16k 18k 20k 22.4k

DF-55 Guaranteed Specifications[Guaranteed specifications measured in compliance with JEITA standard method CP-2402A]

Divider units
Channel A

q

Channel B

w eChannel C

Channel D

r ty

u i

o

ChannelD

ChannelC

ChannelB● Digital inputs
COAXIAL
Format:IEC 60958/AES3 compliant
Sampling frequencies 32 kHz to 192 kHz (16 - 24 bit 2-channel PCM)
OPTICAL
Format:JEITA CP-1212
Sampling frequencies 32 kHz to 96 kHz (16 - 24 bit 2-channel PCM)
HS-LINK
Connector:
RJ-45, HS-Link cable
Sampling frequencies 32 kHz to 192 kHz (24 bit 2-channel PCM)
● Analog inputs
Maximum input level 3.7 V (1 kHz, 2.5 V output)
A/D converter
Principle:
1-bit delta sigma modulation
Sampling frequency: 176.4 kHz
Quantization:
24 bit● Digital outputs
HS-LINK
Connector: RJ-45, HS-Link cable
COAXIAL
Format:IEC 60958● Frequency response
HS-Link 2.0 - 50,000 Hz +0 -3 dB● D/A converter
Quantization:
24 bit
STEREO operation: 4MDS++ type
MONO operation:
8MDS++ type
● THD
0.001% (20 - 20,000 Hz)● S/N ratio
STEREO operation MONO operation

COAXIAL/OPTICAL
HS-LINK
Analog input

Analog outputs（LINE/BALANCED）■ Rear panelt2

b is delayed by [t3 - t2] seconds○〔Channel C〕) symbol at top right of level indication is shown when "Full Level Output Protection" function is set to ON.

■ Front panel

When ON:
Delayed by
t3 - t2 seconds

2

STEREO*(ON

by t2 secondscversus ○Delay: t s(Band-pass filter)

Display
indication
ディスプレイUPPER FREQUENCYb
Output○a compensation time)(○〔Channel A〕

3〔Channel B〕

c are delayed, using
b and ○○a as reference ○0
slowest ○0

Delay: t s■ DF-55 default settings and display indication
LOWER FREQUENCY

When DELAY COMP is ON
ON or OFF

When OFF:a is slowest, delayed○cby t3 seconds versus ○(Low-pass filter)

The DF-55 calculates and displays thetheoretical delay time, and automaticallyprovides compensation. (Default setting)
The DF-55 calculates and displays thetheoretical delay time for reference, and theuser can manually set any desired value.

Function機
能a
Output○Time lag (delay) of output signal withregard to input in each channel● Dynamic range● Channel separation● Slope characteristics

ChannelA

120 dB
120 dB
113 dB

122 dB
122 dB114 dB"Analog ATT" OFF: 117 dB, "Analog ATT" ON: 114 dB
108 dB (20 - 20,000 Hz)
6 dB/octave, 12 dB/octave, 18 dB/octave
24 dB/octave, 48 dB/octave, 96 dB/octave* When cutoff frequency is 10 Hz: 48 dB/octave, 96 dB/octave not available
20 Hz: 96 dB/octave not available!0 ★
q POWER switch
w FUNCTION knob (To select a function)e ENCODER knob (To set the value)r Input selectort Memory selectory Display
INPUT: BAL, LINE, HS-LINK, COAX, OPTOMEMORY: 1, 2, 3, 4, 5

u Digital inputs
HS-LINK, COAXIAL, OPTICAL
i Digital output
HS-LINKo Analog inputs
LINE, BALANCED!0 AC power connector ★
(for supplied power cord)● Delay setting range-3,000 to +3,000 cm (0.5-cm steps)(converted into distance)● Level adjustment range "Analog ATT" OFF: -40 to +12.0 dB (0.1-dB steps)"Analog ATT" ON: -50 to +2.0 dB (0.1-dB steps)● Output voltage/output LINE: 2.5 V, 50 ohms, RCA-type phono connector
impedance
BALANCED: 2.5 V, 50 ohms, balanced XLR connector● Minimum load impedance LINE/BALANCED 600 ohms
● Power requirements
AC 120 V/230 V, 50/60 Hz (Voltage as indicated on rear panel)● Power consumption
29 watts● Max. dimensions
Width
465 mm (18-5/16")
Height 151 mm (5-15/16")
Depth
396 mm (15-9/16")● Mass
14.7 kg (32.4 lbs) net
20.0 kg (44.1 lbs) in shipping carton

Remarks★ This product is available in versions for 120/230 V AC. Make sure that the voltage shown on the rear panel matches the AC line voltage in your area.
★ The shape of the AC inlet and plug of the supplied power cord depends on the voltage rating and destination country.
■ Supplied accessory●●

AC power cord

Specifications and design subject to change without notice for improvements.
A1105YPRINTED IN JAPAN 851-0202-00（B1）