Cedar DH-1 De-Hisster User manual

Professional Hardware Systems
DH-1 De-Hisser
Digital Audio Restoration System
SERIES 2
OWNER'S MANUAL
© 1994 CEDAR Audio Ltd. Written by Gordon Reid
DH- 1: Rev.02 Ver. 1.06
Page - 1
July 12, 1996

TABLE OF CONTENTS
TABLE OF CONTENTS.............................................................................................2
INTRODUCTION ........................................................................................................3
THE
BACKGROUND TO CEDAR NOISE REMOVAL.....................................4
SAFETY INSTRUCTIONS .................................... ... ..................................................9
SET
UP ........................................................................................................................... 11
Unpacking and Inspection............................................................................. 11
Installation site.................................................................................................. 11
Rack Mounting ............................................ .. ................................................... 11
Free Standing use ............................................................................................. 11
CONNECTIONS ..........................................................................................................12
Before
Connection ....................................... ... .................................................12
Power Connections ............................. .. ....................................... ... .................12
Signal
Lead Connections ................................................................................12
Other Connections ................................... .. .......... .. ..........................................14
SAMPLE INSTALLATION IDEAS.........................................................................15
A GUIDE
TO RESTORATION PROCESSING .. ............................... .. ..................16
FRONT
PANEL INDICATORS AND CONTROLS............................................. 18
QUICK TOUR...................................................... ... ............ ... .......................................20
WARMSTART
AND COLDSTART....................................................................... .21
OPERATING THE CEDAR DH-1............... .. ....... ... .................................................22
Dedica ted Con troIs ................. .... .... .. ..............................................................22
PAGES ...............................................................................................................24
Con trol Page ......................................................................................... 25
Input/Output Control Page .............................................................. 28
Remote Con trol ....................................................................................32
Status Page .......... .. .... .... .............. .. ........................................................33
Status Indicators...................................................................................33
TUTORIAL.....................
... ..... .. ...................... .. .............................................................35
THE TUTORIAL TAPE..............................................................................................38
REMOTE
CONTROL PROTOCOLS....... .. . ... ..........................................................39
RS232...................................................................................................................39
MIDI..............................................
.. .................................................................... 41
SELF TEST MODE ..................... ... .... ... .... .......... ... ..... .. ...............................................42
DH-1: Rev.02 Ver.1.06
Page-2
July 12,1996

INTRODUCTION
Thank you for purchasing the CEDAR DH-1 De-Hisser Module. This is the world's
most advanced dedicated single-ended noise removal unit, and offers processing
power and performance that could only previously be obtained using digital signal
processors (DSPs) installed
in desk-top (or larger) computer systems such as the
CEDAR Production System. The De-Hisser is designed for professional use,
although it will work perfectly well
in a domestic environment, and its features
include the following:
Revolutionary noise removal algorithms
• No need for a "Spectral Fingerprint"
• The latest 'SERIES-2' CEDAR hardware
Digital Audio interfaces conforming to the AES/EBU and SP-DIF standards
24-bit input and output resolution when using AES/EBU interfaces
• Three sample rates supported
on digital inputs: 32kHz, 44.1 kHz and 48kHz
• Two sample rates supported
on analogue inputs: 44.1 kHz and 48kHz
• Balanced analogue inputs and outputs for connection to professional
analogue equipment
• ADC and DAC converters using the latest 64x over-sampling
~- I. (Delta-
Sigma) technology
• >103dB dynamic range AID and >93dB dynamic range D/A
Mountable in a 19" EIA rack
• Remote control via MIDI and RS232 interfaces
• SMPTE/EBU timecode capabilities via optional upgrade
• Input and output LED bar-graph
VU meters
Twin 40-bit floating point DSP processors delivering 50MFIops to handle the
most complex audio processing requirements
• High levels of artificial intelligence designed into the DH-1 program
algorithms making
it extremely simple to use
DH-1: Rev . 02 Ver.1 . 06
Page - 3
July 12. 1996

THE BACKGROUND TO CEDAR NOISE REMOVAL
Cheap digital audio (i.e. CD) has made discerning listeners quite intolerant of the
noises and distortions present
in analogue audio signals. After all, in a perfect
digital world there are
no clicks, crackle, pops, buzzes or hums, and no hiss - so it's
a shame that we live
in a far from perfect world. Even today, the vast majority of
mixing desks still have all-analogue signal paths, so most DOD-classified CDs are
still mastered through numerous analogue stages. And 'vintage' (i.e. pre-1982)
recordings are
by definition re-mastered from analogue master tapes which
inevitably suffer from at least one of the degradations listed above. So recording
engineers are turning more and more
to the technologies available for reducing
any noise added in the signal path, or for removing it from the final recording.
You can
rid yourself of any broadband noise you care to mention ... white noise,
tape hiss, microphone noise, rumbles
... you name it, you can eliminate it. Totally,
and without any fuss or expensive equipment. How? Simple
... by turning your
master volume control to zero. OK,
so this method also has a rather drastic effect on
the signal content of your recording - it completely removes it -but what do you
mean, you want to get rid of all the noise but keep the genuine signal absolutely
untouched?
Before proceeding any further, perhaps it would
be best to describe what we mean
by the term 'broadband' noise. Such noise is, by definition, a random effect which
adds (or subtracts) a random amplitude at all times to (or from) all frequencies
within the audio spectrum. Thus, the term
is used inappropriately to describe
artefacts such as intermittent electrical clicks or microphone 'grounding'. These
problems produce clearly identifiable events of limited duration, and may be
corrected
by the CEDAR DC-1 De-Clicker and CR-1 De-Crackler using quite
different methods to those described below. On the other hand, broadband noise
is
constantly present (to a greater or lesser degree) in every signal. It is often most
intrusive at high frequencies, where the masking effect of loud sounds is least
present,
so the term 'hiss' is often used to describe all forms of broadband noise.
Firstly, let's dispel any illusions regarding the Dolby
B, Dolby C, and dbx noise
reduction systems. These are dual-ended processes designed to minimise the
accumulation of any extra noise added by the limitations of analogue recording
tape. (Dual-ended processes are commonly called encode/decode systems
because the recording process 'encodes', and the playback process 'decodes', the
signal.) Neither the Dolby processes nor dbx enable you to remove noise from
within a signal that already contains
it -they simply stop you adding too much more
when you commit that signal to tape and then play
it back again. Perversely then,
both Dolby and dbx help your tape deck to accurately record, and then faithfully
reproduce, any noise contained
in the original signal. So, what you need is a
'single-ended' process that can remove noise from your signals prior to committing
them
to tape, or at the very least, can improve the signal to noise (S/N) ratio without
affecting the signal adversely. Which brings us neatly back
to the volume control. ..
stunningly effective at removing noise, it does nothing to improve the SIN ratio, and
has
an all-too-noticeable side-effect. No noise, No signal.
DH- 1: Rev.02 Ver .1.06
Page-4
July 12.1996

The first stage in our evolutionary tale of noise removal is the simple treble filter (or
'low-pass filter'). Less damaging than the volume control which removes the signal
a!together, the treble filter only removes a proportion of any signal present above a
g~ven frequency (known as the shelf frequency of the filter). Unfortunately, if, at the
given frequency, you reduce the amplitude of the noise content of your recording
by 6d8 (thus making the noise half as loud) you will also reduce the genuine signal
at this frequency by the same amount. This will be fine if your recording has little or
no high frequency content, but natural sounds and modern electronic instruments
have frequency responses up to and beyond the limits of human hearing.
Consequently, the treble filter will only be successful
in processing your antique
collection of '78's, and even then only
at a cost.
But this gives us a hint as to how a more effective single-ended noise reduction
system could
be designed: perhaps a device could be built which removes the high
frequencies when there
is no signal present, but leaves them untouched when the
noise is being masked by genuine high frequencies? Of course it can. It's a
Dynamic Filter (so called because the shelf frequency of the filter moves
dynamically up and down the frequency spectrum according to information
contained
in the signal). But such devices are limited: for one thing, they can only
remove the noise which exists above the highest frequency of the music present at
any given moment. Secondly, they are based
on filters with roll-offs typically of the
order -12d8/0ctave or -6dB/octave,
so they always allow some high frequencies
through, even when they think that they're removing
it. And thirdly, even though the
filters are designed to track the signal very quickly, they cannot respond
instantaneously, so they tend to round off fast transients such as snare drums and
samples (which have a habit of introducing high frequencies very rapidly into the
signal). And, because their raison d'etre is to reduce the signal bandwidth they also
tend to dull the genuine signal quite perceptibly. So
to summarise dynamic filters: if
you're not compromising the signal you may not
be removing as much noise as
you wish, and if you're removing all the noise you're probably damaging the
genuine signal.
Perhaps an alternative approach could give better results? Instead of altering the
frequency response of the signal to reduce the noise content, how about changing
the volume (amplitude response) of the signal
in some way? This isn't such a
strange idea. Consider: if noise is always present
in a signal then, if the total signal
amplitude drops down to the noise level, surely all the genuine musical signal has
disappeared? While there are many flaws
in this argument (largely to do with the
statistical nature of broadband noise)
it is, as a generalisation, nearly true. This
then suggests a device which will eliminate some of the noise: a Noise Gate. This
simple device detects when the signal drops below a certain level (a 'threshold' set
by the user) and then cuts off the signal entirely. It's just like turning the volume
control of your hi-fi to zero between tracks, and then turning
it back up at exactly the
moment the music starts again. There are many enhancements to the Gate idea,
such
as variable attack and release times, and hysteresis (all added to limit the
occurrence of damaging side-effects) but the principle always remains the same: if
the device decides that there is only noise present at its input,
it totally shuts off the
signal. There
is an adage that says that a multi-track studio can never have too
many noise gates because, while they are pretty useless at stereo mastering, they
are invaluable for shutting off the intrusive hisses, hums, and buzzes of temporarily
unused synths and guitar channels.
DH- 1: Rev.02 Ver. 1.06 Page - 5
July 12.1996

Unfortunately, though the Noise Gate sounds great in theory, it doesn't sound so
great in reality. It has a distinct advantage over the low-pass filter (after all, it
removes all the frequencies of broadband noise, not just the high ones) but once
the gate is 'open' all the noise comes flooding back. And if you adjust the threshold
so that noise can only come through when the signal is loud enough to mask it,
you'll lose the ability
to include quiet passages in your recordings. So the Noise
Gate is as damaging its own way as the filter is
in its. Fortunately, just as the filter
can be improved by making it dynamic,
so c"an the gate. Such a device is called an
Expander and its operation is a bit like that of a compressor, but in reverse. The
Expander still has a threshold control, but unlike the gate (which shuts the volume
down to zero once the threshold
is passed) the Expander applies a progressive
gain reduction, the amount of which is determined by the settings selected by the
user. For example, if a signal drops 3dB below the threshold, the Expander may
reduce the signal volume by 6dB, 12dB, or any other figure, depending upon the
expansion ratio requested. Unfortunately, many audio professionals claim that the
subjective difference between the true noise gate and the expander are very small
-and you wouldn't use either for top quality recording or mastering.
Some of the more highly specified noise reduction units now feature a combination
of dynamic filtering, expansion, and even compression and excitation -effects
which have been included
to overcome some of the undesirable side-effects of the
noise reduction processes. But they are only partially successful when cleaning up
complete mixes, and you still can't master full bandwidth CDs or film soundtracks
with them. The results simply aren't good enough.
Now, consider what happens when the single-band expander described above
encounters a very quiet signal.
.. it further reduces the volume. But what if there is
still a significant signal
at (say) 3kHz, but very little elsewhere in the frequency
spectrum? The single band expander has
no way of knowing that there's an
important genuine signal within a limited range, and
it shuts this out at the same
time as all other frequencies. What's needed is
an expander which can detect such
instances, and cope with them appropriately. A mUlti-band unit does this by
separating the audio spectrum into a number of bands, and then treating each of
these as individual signals. Consequently, such a device can be reducing the
volume
in one band, while passing the signal untouched in other bands. This type
of noise reduction has now found its way from rackmount modules onto computers.
Digital Audio Workstations (usually hard disk editors with other functions added)
utilise processor chips known as Digital Signal Processors (DSPs) which perform
millions of calculations every second upon the audio data produced by CD players,
DAT machines, and Analogue-to-Digital Converters. Splitting the audio spectrum
up into multiple bands is simple for such devices, and applying expansion
in the
digital domain is a straightforward process compared to some of the more esoteric
DSP functions. But even multi-band units have no way to make a true distinction
between signal and noise. They still act upon the mistaken assumption that, if the
signal level approaches its noise floor, all that is present is broadband noise.
Consequently, even the most sophisticated downwards expanders and dynamic
filters inevitably remove some of the genuine signal. The consequences of this are
well understood and, to a greater or lesser extent, unavoidable: loss of high
frequencies, loss of ambience, and degradation of hard transients.
So we finally arrive at the most sophisticated noi
se removal technology yet
implemented: Spectral Subtraction. But to explain what this
is we must first dive
into a little simple mathematics
...
DH- 1: Rev. 02 Ver.1.06 Page - 6
July 12. 1996

All the methods and products described above use filters, gain controls, or a
combination
of both to achieve their results. Whether implemented in the analogue
or digital domains, all such filters and gain controls are 'ratio' devices -that is, if (at
any given frequency) you remove half the power of the noise, you remove half the
power of the signal at that same frequency; if you remove 3/4 of the noise, you
remove 3/4
of the signal ... and so on. But now let's consider what else is possible in
the digital domain: Imagine a signal that has, at a given frequency, 100 units of
'volume'
on some arbitrary scale. Let's also say that, by measuring the noise
content of the signal during
an otherwise silent moment, you have determined that
there are 20 units of noise present on the same scale.
It should be possible to
remove the noise amplitude by subtracting these 20 units (in the digital domain) or
by filtering out 20% of the signal
in the analogue domain. But what if, a moment
later, the 'volume' of the signal drops to 40 units? The analogue filter, set to 20%
reduction, will only remove 8 units of noise, whereas the digital process is still able
to remove the full 20 units (equivalent to a filter reduction of 50%). This is, of
course, what
we want, because the noise now represents, in fact, 50% of the total
signal amplitude. No analogue device can precisely emUlate this 'subtractive' filter,
and herein lies the power of the computerised noise reduction system.
Computers can, among other things, split the audio signal into hundreds of very
narrow bands, and apply Spectral Subtraction
to each of these. Splitting the signal
this way means that you can
be very precise about how much noise you remove,
subtracting a lot
at (say) 8kHz, while leaving 8.1 kHz virtually untouched. Sounds
too good
to be true? Unfortunately, it is. The noise spectrum of a recording (the
spectral fingerprint) can only be accurately measured if there is an otherwise silent
passage within the music.
If the fingerprint is wrong (maybe because you have
captured some lingering reverb, or because a compressor has been applied
at
some time, or because the original recording engineer has faded sections in and
out of the recording) the amount subtracted will
be wrong, leading to some very
unpleasant sounding side-effects. And, just to make matters worse, many tracks are
'close edited' -the run-in and run-out of the track have been removed -making
it
impossible to take a fingerprint.
Let's assume that you have a perfect fingerprint. You might expect to produce a
very good restoration of your track: large amounts of noise removed, with little or
no
side-effects. Yet experience shows that all attempts to use an unmodified noise
fingerprint lead to a dry and dull sounding result. This is because the fingerprint is
merely a snapshot of the noise content of the material, accurate only
at the instant
at which
it is taken. The very essence of noise is its random nature, and because
the profile of the noise content is constantly changing,
it is necessary for the noise
fingerprint within the system
to change as well. Which brings us to CEDAR HISS-2.
With a noise fingerprint that is updated 44 times per second (allowing CEDAR
to
track variations in the noise content of the recording); algorithms which 'Iook-
ahead' at the incoming signal, responding
to transients before they occur; and an
ambience control which ensures that sounds are not prematurely cut short, CEDAR
combines many of the analogue and digital ideas discussed above. This means
that,
in theory at least, the amount of noise being removed is always appropriate.
Consequently, HISS-2 avoids the pitfalls and finally enables the user
to remove the
right amount of noise without damaging the source signal.
DH- 1: Rev.02 Ver.1.06 Page - 7
July 12. 1996

But HISS-2 cannot be implemented in a stand-alone box such as the DH-1. It still
requires a noise fingerprint, whether captured from the signal or created by the
CEDAR operator. (This requirement
is almost the sole reason for the 5 years of
further research that has occurred since the launch of the original
CEDAR Noise
Reduction System and the DH-1.) The DH-1 includes revolutionary new algorithms
which have finally dispensed with this requirement, enabling you to remove noise
in a powerful, yet automated, fashion. The DH-1 will itself analyse the noise content
of a signal (whether genuine sound is present or not!) and apply all the power of
CEDAR's latest noise removal algorithms to this signal.
The results speak for themselves.
Dolby S, Dolby C, and db x are trademarks of their respective manufacturers,
Page - 8
DH- 1: Rev,02 Ver.1 ,06
July 12, 1996

SAFETY INSTRUCTIONS
CAUTION:
1 . Read all of these instructions
All safety and operating instructions should be read before the DH-1 is
operated.
2. Save these instructions for future reference.
3. Follow all warnings and instructions.
4. Water and Moisture
The DH-1 should not be used near water, and must not be exposed to rain
or moisture.
If the DH-1 is brought directly from a cold environment into a
warm one, moisture may condense inside the unit. This, in itself, will not
damage the DH-1, but may cause hazardous electrical shorting to occur.
This could severely damage the DH-1, and even cause
danger to life.
ALWAYS allow time for the DH-1 to naturally reach ambient temperatures
before connecting the mains power.
5. Mounting
The DH-1 should be carefully mounted in a 19" EIA rack, or placed on a flat,
stable surface.
If used on a cart or free stand, care should be taken when
moved: uneven surfaces or excessive force may cause cart and DH-1 to
overturn. Do not position the DH-1
in a place subject to strong sunlight,
excessive dust, mechanical vibration or periodic shocks.
6. Wall or
Ceiling Mounting
The DH-1 has not been designed for mounting directly to walls or ceilings.
7. Ventilation
Good air circulation is essential to prevent internal heat build-up within the
DH-1. The DH-1 should be situated so that its position
does not interfere with
proper ventilation.
The DH-1 should not be placed in any situation which
impedes the flow of air through the vents at the front and rear. Do not place
the DH-1 on a soft surface.
8. External Heat Sources
The DH-1 should be installed away from significant heat sources such as
radiators, and (if possible) away from other audio devices such as amplifiers
that produce large amounts of heat. Installation
in racks with devices such as
signal processors or tape machines should not be a problem.
9. Power Sources
The DH-1 features an auto-switching power supply which will work safely on
any mains supply
in the ranges 95v/130v and 190v/260v, 50Hz or 60Hz AC
only.
You should never attempt to modify or adjust the internal power
supply in any way. It contains no user serviceable parts.
DH- 1: Rev.02 Ver. 1. 06 Page - 9
July 12, 1996

10. Grounding or Polarisation
The DH-1 should always be grounded (or 'earthed').
11. Power Cord Protection
Power connectors should be routed so that they will not be walked on or
pinched.
12. Extended Periods of Non-Use
The DH-1 is not disconnected from the mains power as long as it is
connected to the wall outlet, even if the unit itself has been switched off.
Therefore, if the DH-1 is not to be used for an
extended period of time,
unplug the unit from the wall. Pull the
connector out by the plug, never by the
cord itself.
13.
Cleaning
Clean only with a dry cloth. NEVER use liquid cleaners such as alcohol or
benzene on the DH-1. NEVER use abrasive pads on the DH-1.
14.
Damage Requiring Service
The DH-1 should be returned to qualified service personnel when:
objects have fallen into the unit
• liquid has been spilled into the unit
• the unit has been
exposed to rain
• the unit fails to function or appears to
operate abnormally
• the unit has been dropped, or the case damaged.
15. Servicing
The user should not attempt to service the DH-1 beyond the instructions
contained in the User's Manual. All other servicing should be referred to
qualified service personnel.
DH-l: Rev.02 Ver.1.06 Page -
10
July 12. 1996

SET UP
1. UNPACKING AND INSPECTION
Be careful not to damage the DH-1 during unpacking. Save the carton and
all packing materials since you may need them to transport the DH-1
in the
future.
In addition to the packaging, the carton should contain the following:
• mains connection lead
• this manual
• blanking plates which may
be used to replace the rack-mount ears
• DH-1 Tutorial OAT
2. INSTALLATION SITE
The DH-1 may be used in most areas, but to maintain reliability and prolong
operating life observe the following environmental considerations:
• Nominal temperature should
be maintained between 5' and 35'
Centigrade (41' and 95' Fahrenheit).
• Relative humidity should be in the range 30% to 60% non-
condensing.
• Strong magnetic fields should not exist nearby.
3. RACK MOUNTING
The DH-1 can be mounted in a standard 19" EIA rack.
4. FREE STANDING USE
The DH-1 can be used as a free-standing unit. The rack-mount ears may
then be replaced by the blanking plates if desired.
To replace the ears with the blanking plates:
• Unscrew the three bolts which attach each ear to the chassis of the
DH-1.
• Attach the blanking plates using the same retaining bolts. Do not
over-tighten these bolts as doing so may cause
damage to the DH-1.
DH-1: Rev.02 Ver.1.06 Page -
11
July 12, 1996

Power
Balanced Balanced Connector
Timecode
Analogue Analogue with integral
Input and Output
Inputs Outputs fuse holder
I
LTC VITC
..
• j j •
•
•
R - IN -L R - OUT - L IN -LTC -OUT
IN -VITC -OUT
.g~
o~
QQI·~Q
AES - IN
~g
0
-SPDlF SPDIF -OUT -AES
o
~
o
~
-.
J
Digital 110
SP-DIF
Q
o ..
o 0
o o
IN
©
OO
o 0
o
OUT THRU
©
oo ©oo
o 0 0 0
o 0
I
o 0
RS 232 INTERFACE
00
0
1
•
I
• CAUTION
00 NOT OPEN •
POWER
HO USE ,,"SERVICEABLE PAR TS INSIOE ~
RISK Of' ElECTR IC SHOCK [3
!h Lh · t'=j .
Serial No: •
I MIDI
In/OutlThru RS232
Interface
Digital 1/0
AES/EBU

CONNECTIONS
The DH-1 may be connected to most of the professional audio equipment currently
available. Three types of audio input and output are provided (one analogue and
two digital) and these will satisfy most users' interconnection requirements. Full
descriptions of these connectors will
be found later in the manual.
1. BEFORE CONNECTION
• To prevent problems and possible equipment damage, turn off the
power to all equipment before making connections.
•
Be sure to insert plugs firmly into sockets. Loose connections may
cause hum and noise.
• When unplugging any lead, do
so by grasping the plug, not the lead.
2. POWER CONNECTIONS
Ensure that the DH-1 is switched OFF before inserting the mains lead.
NOTE: Users with 2-pin mains supplies:
When the DH-1 is connected to other audio components, the AC hum of the
unit may
be increased or decreased by reversing the direction of the power
connector in the socket. Check that the cord
is in the favourable position Cin-
phase') with respect to other audio devices in the chain. This will ensure that
the best sound quality is obtained from your DH-1.
For further information
on grounding and polarity consult a person familiar
with studio grounding techniques.
3. SIGNAL LEAD CONNECTIONS
Refer to the Rear Panel diagram:
The
DH-1 offers three audio connection standards: one analogue and two
digital. These are:
• balanced analogue audio I/O
digital SP-DIF format audio data
digital AES/EBU format audio data
Note that the OH-1 always passes its output to all three signal outputs
irrespective
of the input used, but that the digital data will only be formatted
for either
AES IEBU or SP-OIF, as defined by the user parameters.
DH- 1: Rev.02 Ver. l.06
Page - 12
July 12.1996

(i)
Balanced analogue audio 1/0 (Pin 2 - 'hot')
This standard is used in professional audio equipment. Connect the
output from your source to the balanced analogue inputs of the
DH-1
using standard XLR plugs. You will require two such connections: one
for each channel.
The balanced audio output may be used to connect the DH-1 directly
to audio equipment such as mixing desks and professional recorders
featuring balanced XLR inputs and outputs.
(ii) Digital SP-DIF format audio data
The SP-DIF format is used by domestic and semi-professional digital
audio devices such as OAT machines, some ADCs, and some CD
players. Both audio channels are carried along a single cable, so you
may connect the SP-DIF output from your source to the SP-DIF input
of the
DH-1 using a single cable terminated with RCA (or 'phono')
plugs.
The SP-DIF output of the
DH-1 may be connected to the SP-DIF input
of
your recording device or external DAC.
(iii) Digital AES/EBU format audio data
The digital AES/EBU format is used by professional digital audio
devices including mastering systems, DASH recorders, and high
quality ADCs & DACs. Both channels of audio are carried along a
single cable, so you may connect the AES/EBU output from your
source to the AES/EBU input of the DH-1 using a single cable
terminated with XLR plugs.
The AES/EBU output of the
DH-1 may be connected to the AES/EBU
input of your digital mixer, recording device or external DAC.
24-bit Digital data resolution:
The DH-1 features 24-bit input and output resolution whenever the
AES/EBU digital input and output are utilised.
Dithering:
The DH-1 SERIES 2 also features TPDF (Triangular Probability
Density Function) dithering. This is applied to the digital data when
the SP-DIF output format is selected. Dithering is always applied to
the data presented
to the DACs.
In order to fully comply with EMC regulations, this unit should be connected
via its
AES/EBU and/or analogue connectors. Metal-shelled XLR
connectors should be used.
We recommend using a good quality 'starquad'
cable, with three cores connected
to pins 1, 2 & 3. The shield of the cable
should be connected, at both ends,
to the outer shell of the connector.
DH-l: Rev.02 Ver.l . 06
Page - 13
July 12,1996

4. OTHER CONNECTIONS
(i) SMPTE/EBU
An optional SMPTE/EBU interface offering LTC and VITC protocols is
available for the DH-1. The standard DH-1 does not support timecode
and these connectors are not present.
(ii) MIDI IN/OUTITHRU
The operation of the DH-1 may be controlled using the Musical
Instrument Digital Interface (MIDI). Refer to the chapter on Remote
Control Protocols for further instructions.
(iii) RS232
The DH-1 may be controlled using the standard RS232 serial
communications protocol. Refer to the chapter on Remote Control
Protocols for further instructions.
DH- 1: Rev.02 Ver.1 . 06
Page - 14
July 12. 1996

- -
--
--
--
SAMPLE INSTALLATION IDEAS
an al O() ue or
l
in eo ut digilal in
di gi ia lo ul
ana log<.e or analog ue or
di gll al in
TURNTABLE 0
TAPE MACHINE
AMP
DH·l -
lim in
RECORDER
1. OH-1 used in-line for transcription or broadcast purposes.
anaklg ue or ana l og ue or
a na log ue or
l im out
d igila l in dlg ii alo ul
di gita l in
SOURCE
RECORDER
MIXER e ll ec ls relU rn
line in
line oul l
AMP
DH·l
2. OH-1 used on the effects loop within a studio environment.
analogue or a
nalogue or
anabgu eor a nal og ue or
an al ogue or
l
ine ou l d ig ll alin
dig ii al o ul digi lal in di gna loul
di gi lal in
DH ·l
r-----
CEDAR
"---r---+.- RECORDER
I.. SOURCE ::Jt-
Dr OI lie r 'rYorKSlalio n iedilo(
-l
in ein
AMP
3. OH-1 used in-line prior to an editor or audio workstation.
DH-1 : Rev.02 Ver .1.06
Page - 15
July 12,1996

A GUIDE TO RESTORATION PROCESSING
Contrary to 'common sense', the order in which restoration processes are carried
out makes a great deal of difference to the quality of the final result. Consequently,
there is one 'right way' and many 'wrong ways' to restore your material.
Following these guidelines will help you
to achieve the best results on most
material:
• De-Clicking (De-Scratching) should ALWAYS be carried out first. This is
because:
Large clicks make
it difficult for the De-Crackling process to identify
and remove the tiny clicks and crackles that constitute surface noise,
buzz, and other such problems.
ii All clicks and scratches are,
in effect, tightly defined packets of white
noise.
If clicks are presented to any of the CEDAR De-Hiss products
(HISS-1, HISS-2,
DH-1 De-Hiss) they confuse the processes, and
create unmusical side effects.
In addition, De-Hissing at this stage will
make
it almost impossible to identify and remove clicks and scratches
at a later time.
• De-Crackling should be the next process because even small crackles can
cause the same problems as
in (ii) above.
• Azimuth Correction can be carried out either before or after De-Hissing, but
experience shows that best results are obtained using the
AZ-1 or Phase-EX
module before De-Hiss.
• Finally, apply whichever De-Hiss process you wish to use.
Note: If you have the full range of CEDAR restoration modules they should be
connected as shown
in the diagram overleaf. Please note that, to maintain
the maximum fidelity
and remove and possible sources of degradation
between processes, connections between modules
should be by AESIEBU
(24-bit) format.
DH- 1: Rev.02 Ver .1.06
Page - 16
July 12.1996

Firstly, De-Click your material
Next, remove crackle
and buzz, and reduce distortion if appropriate
Then applyAzimuth Correction to material with phase
and balance problems
Finally, applynoise reduction.
DH-1 : Rev.02 Ver .1.06
Page - 17
July
12, 1996

(0
CD CD
0
CD
(0
0
Input
Output
Defined
a-dial
Power Signal Signal
LCD
Status Function Control
Switch Meters Meters Screen
Indicators
Keys
Wheel
Headphone
Level
Control
CD
Headphones
Socket
CD
Input
Level
Control
®
Output
Attenuation
Control
@
ttl 1 t
Fl
F2 F3 F4 F5
I
Function Contrast
Keys
Control
@ ®

LOCATION AND FUNCTION OF FRONT PANEL
INDICATORS AND CONTROLS
Refer to the Front Panel diagram:
1 . Power Switch
2. Input Signal Meters (Left and Right)
Digital signal meters display the peak value of the selected input in dBOs.
The 'Over' indicators will light if the input signal remains at full scale for four
or more consecutive samples.
3. Output Signal Meters (Left and Right)
Calibrated signal meters display the RMS value of all output signals.
The 'Over' indicators will light if the output signal remains at full scale for four
or more consecutive samples.
4. LCD Screen
Provides you with a variety of information and messages, keeping you
aware of what
is currently happening in the DH-1.
All the control screens of the DH-1 are displayed
on the LCD screen. Please
refer to the following chapters for full instructions.
5. Status Indicators
Indicate the status of the analogue and digital inputs, and whether the DH-1
SERIES 2 is in idle or processing modes.
Also indicate the possible causes should the unit fail to function.
6. Dedicated Function Keys.
Certain functions are fundamental to operating the DH-1, and these are
controlled by the Dedicated function keys: Bypass, Page, Pre/Post, and
Enter.
7. a-dial (Spinwheel)
The a-dial enables you to increase and decrease control values. Please
refer to the following chapters for full instructions.
8. Headphone Socket
For use with stereo headphones only. Accepts a standard 1/4" stereo jack
plug. DO NOT use 2-conductor mono headphones with the DH-1.
9. Headphone Level Control
Use this to adjust for a satisfactory listening level. This level control will not
alter the signal level at any of the rear panel outputs.
DH-1 : Rev. 02 Ver.1 . 06
Page - 18
July 12. 1996