Grimm Audio AD1 User manual

Please read this manual before operating the unit!

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Table of Contents
Important Safety Instructions 5
1. Installing 7
2. Signal connections 8
3. About DSD 10
4. Specifications 13
5. Grimm Audio Limited Waranty 15

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Introduction
Thank you for choosing the Grimm Audio AD1 DSD AD converter for your produc-
tion. This product embodies our company philosophy of providing the most trans-
parent and direct signal chain possible, enabling you to achieve the best possible
results sonically and artistically.
This manual describes how to set up the unit in your studio as well as important
tips on how to get the best performance from the AD1. In addition, some back-
ground information on the unitʼs operation is provided.
We have taken pains to insure that the manual is up to date and clear. Should you
have any further questions or suggestions on how to improve this manual, please
feel welcome to get in touch with us.
We hope this investment will bring you many years of creative enjoyment and help
you achieve your goals.

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Important Safety Instructions
Grimm Audio gaat er van uit dat u deze Engelstalige tekst volledig begrijpt. Als u hier moeite
mee heeft dient u contact op te nemen met Grimm Audio. Op verzoek sturen wij u een vertaling
toe.
Grimm Audio nimmt an, dass Sie diesen Englischen Text völlig verstehen. Wenn notwendig,
nehmen Sie bitte Kontakt auf mit Grimm Audio. Auf Wünsch wird Ihnen eine Übersetzung zu-
geschickt.
Grimm Audio suppose que le lecteur comprend parfaitement le texte en Anglais ci-dessous. En
cas de doute s.v.p. contacter Grimm Audio. Si necessaire, on pourra vous envoyer une traduc-
tion.
Grimm Audio da por supuesto que el texto en versión Inglesa no ofrece ninguna duda de in-
terpretación y se entiende integramente. Si este no fuese su caso rogamos contacte con Grimm
Audio quien, a petición, se encargaría de enviarle la correspondiente traducción.
Please follow these precautions when using this product:
1. Read these instructions.
2. Keep these instructions.
3. Heed all warnings.
4. Follow all instructions.
5. Dangerous voltage is inside this apparatus. Opening is only allowed by qualified
service personnel.
6. Verify line voltage before use.
7. Do not defeat the safety purpose of the polarized or grounding-type plug. A po-
larized plug has two blades with one wider than the other. A grounding-type plug
has two blades and a third grounding prong. The wide blade or the third prong are
provided for your safety. When the provided plug does not fit into your outlet, con-
sult an electrician for replacement of the obsolete outlet.
8. Protect the power cord from being walked on or pinched, particularly at plugs,
convenience receptables, and the point where they exit from the apparatus.
9. Unplug this apparatus during lightning storms or when unused for long periods
of time.

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10. Do not use this apparatus near water.
11. Do not use this apparatus outside.
12. Do not expose the apparatus to dripping or splashing. Do not place objects
filled with liquids (flower vases, drink cans, coffee cups, etc) on the apparatus.
13. Clean only with a dry, soft, non-fluffy cloth. Do not spray any liquid cleaner
onto the cabinet, as this may lead to dangerous shocks. Do not spray any liquid
cleaner onto the faceplate, as this may damage the front panel.
14. Install in accordance with the manufacturerʼs instructions.
15. Do not install near any heat sources such as radiators, heat registers, stoves, or
other apparatus (including amplifiers) that produce heat. Avoid exposure to direct
sunlight.
16. Use only attachments or accessories specified by the manufacturer.
17. Use only with a cart, stand, bracket, or table designed for use with professional
audio or music equipment. In any installation, make sure that injury or damage will
not result from cables pulling on the apparatus and its mounting. If a cart is used,
use precaution when moving the cart/apparatus combination to avoid injury from
tip-over.
18. This unit runs warm when operated normally. Operate in a well ventilated area
with at least six inches of clearance from peripheral equipment. If this product will
be installed in a rack, make certain there is sufficient air movement within the rack.
Do not place the unit directly on a carpeted surface.
19. This product, in combination with an amplifier and headphones or speakers,
may be capable of producing sound levels that could cause permanent hearing loss.
Do not operate for a long peroid of time at a high volume level or at a level that is
uncomfortable. If you experience any hearing loss or ringing in the ears, you should
consult an audiologist.
20. Refer all servicing to qualified service personnel. Servicing is required when the
apparatus has been damaged in any way, such as when the power-supply cord or
plug is damaged, liquid has been spilled or objects have fallen into the apparatus,
the apparatus has been exposed to rain or moisture, does not operate normally, or
has been dropped.
21. WARNING: To reduce the risk of fire or electric shock, do not expose this appa-
ratus to rain or moisture.

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1. Installing
Unpacking and Inspection
Your AD1 was carefully packed at the factory and the carton it came in was de-
signed to protect it from the trials and tribulations of shipping. Keep the box and all
packing materials, so that in the unlikely event that you need to return the AD1 for
servicing, you can do so safely.
Mounting the AD1
The AD1 can mount in any standard 19” rack. Make sure you leave at least 1U of
space above and below the AD1, and more if the adjacent equipment runs warm.
The AD1 does not produce RF fields nor is susceptible to them. You can position it
near other digital gear such as computer and disk recorders without worry. In gen-
eral it is a good idea to keep some distance between monitors (LCD and CRT) and
audio cables because of risk of low level noise due to stray magnetic fields.
Grimm Audio products have a real wood face plate that provides a beautiful and
vivid appearance. To maintain the outstanding looks, one is advised to take some
precautions:
- Do not place the AD1 in humid nor very dry environments. The wood might crack.
- Do not use chemical or alcohol based cleaner on the wood.
AC Power Hookup
The AD1 has a linear power supply that needs to be factory set for your local line
voltage. Make sure to check the noted line voltage on the back below the IEC cable
entrance (ʻwired for ... Vʼ) and verify that this complies with your locally supplied
line voltage. Grimm Audio cannot be responsible for problems caused by using
the AD1 with improper AC wiring or voltage. Since the AD1 does not have a power
switch on the front panel, a convenient way to power down the unit is to use a
power strip equipped with a switch.

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2. Signal connections
The AD1 is build as a modular system. A chassis can hold both AD and DA boards.
This manual will focus on description of the AD boards. If your unit is equipped
with DA channels, please refer to the DA1 manual that came with your unit.
An AD board offers an analog input on XLR and a DSD format digital output on BNC,
which can be found right above the XLR of the same channel. Although we strongly
advise using balanced connections throughout your whole system, the analog input
is designed such that it will perform equally well on unbalanced audio as on bal-
anced audio. Please pay attention to a proper wiring of unbalanced cables. In the
cable at the source side pin 3 should be connected with pin 1, as can be seen in the
illustration. Unbalanced equipment sporting XLR outputs are normally already wired
in this manner.
Input sensitivity
Your AD1 is calibrated for a 0 DSD level of +18 dBu ±0.1dB. This equals 14 dB of
headroom above a 0 VU defined as +4 dBu, which is common in mastering. Due to
choices made with the ultimate sound quality in mind, this level is factory installed
and cannot be calibrated. If you ordered your AD1 to be calibrated to another level,
it will be indicated on the case.
DSD does not have a defined clipping level like PCM. 0dB DSD is defined as 50%
modulation index (100% modulation index means a constant ʻ1ʼ or ʻ0ʼ output sig-
nal. Hence, 50% modulation means a maximum of 75% or a minimum of 25% of
output samples are ʻ1ʼ). In practice the performance of all 1 bit sigma delta modu-
lators deteriorates very quickly with signals above 0 DSD. One problem is that the
high frequency noise increases severely. The standard for SACD production, ʻScarlet
Bookʼ, demands for a maximum HF noise. The AD1 will conform to Scarlet Book
with signals up to +1.8 dB DSD. Nevertheless we strongly discourage you to drive
the AD1 that hard. First, performance of any DSD AD deteriorates above 0 DSD.
Secondly, the Scarlet book recommends equating 0dBDSD with 0dBFS when deriving
the CD layer on a hybrid disc. This means that levels above 0 DSD will be clipped
on the CD layer. Finally, DA chips in many SACD players do not have any headroom
above 0dBDSD and will clip severely when addressed with signals above 0 DSD. In
chapter ʻAbout DSDʼ on page 10 you will find more information about this subject.

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Clock
On the back of the unit there are two BNC connectors for synchronising the AD1.
Most DSD equipment requires a word clock connection, apart from the SDIF3 data
lines. The upper BNC is a word clock output, the lower one a word clock input. Both
operate at the DSD basic word clock rate of 44.1 kHz. Next to the word clock input
youʼll find three switches that relate to the operation mode of the AD1. The upper
switch selects master mode or slave mode. In slave mode the lower switch selects
what kind of jitter attenuation is used on the incoming word clock. ʻUltraʼ has a jit-
ter suppression down to 0.1 Hz, ʻTightʼ to about a few Hz. Since more jitter attenu-
ation is better, Ultra mode is the preferred choice. Because of fundamental issues
however, latency between the incoming word clock and reclocked output word clock
(and data) can become larger then 20 ns when the incoming jitter is very large. In
Tight mode it will never exceed 20 ns. Sonyʼs SDIF3 specification demands that the
timing of word clock and data is within 20 ns. Many recorders are more tolerant
than this, so Ultra mode will work 95% of the time. If you encounter data sync prob-
lems in slave mode however, you should switch to Tight mode. In that case, please
check your master clock as well, because its jitter appearantly is very high.
The best method is to slave the recorder not to the house sync but to the word
clock output of the AD1. The AD1ʼs clock output and data output are always sync
within 3ns. Some recorders will correctly sync to the embedded clock in the SDIF3
data stream, obviating the need for an explicit word clock connection. Consult the
manual of your recorder for this function.
In slave mode, the white “slave” LED indicates lock. When the unit is locked, the LED
will be continuously on. When the unit is unlocked and while it is acquiring lock,
the LED will blink. Allow several tens of seconds after engaging slave mode for the
circuitry to settle.
The input impedance of the Word Clock input BNC is factory set to ʻHigh imped-
anceʼ. The reason will be explained in the next paragraph. Because of this an exter-
nal 75 Ohm terminator on a T-bar is needed. On demand an internal jumper can be
set to 75 Ohm.
Use of more AD1’s in parallel
To facilitate recording more than 8 channels simultanously, several AD1ʼs can be
synced. In this situation perfect data sync is needed, which means all slaving AD1ʼs
need to be set to ʻTightʼ mode. The word clock inputs of these AD1ʼs are all con-
nected to the word clock output of the first unit, using T-bars on every unit and
terminating with a 75 Ohm terminator on the last one. In this setup the SDIF3 out-
puts of all AD1ʼs are sync within 20 ns.

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3. About DSD
DSD is another word for 1-bit PCM sampled at 2.8224MHz. As a release format,
SACD is the only one actually using this 1-bit data, but as an internal processing
format itʼs surprisingly common. The vast majority of audio converters operate at
1 (or a few bits) at megahertz sampling rates. That means the audio in normal CD
production started its life in a DSD-like format. To get to PCM, digital low-pass
filtering and decimation is required. This is mostly invisible to the user because
converter ICs contain the decimation filter on-board, and put out PCM. But even
if youʼre not aware of it, your PCM converter has quite a bit of DSD-like process-
ing going on inside. Alternatively the decimation can also be done externally in the
Grimm Audio DD1 or a DAW equipped with DSD inputs. Doing so has the benefit of
better control over conversion quality. The filters in converter ICʼs arenʼt optimised
for sound quality but are designed for minimum latency and processing power.
The AD1 runs at the DSD rate of ʻ64 fsʼ (2.8224MHz), which seems like old technol-
ogy in the light of 128 or 256 fs competitors. The higher rate formats however were
designed to get around technical issues related to signal processing in DAWʼs, not
to solve sonic issues in converters. The quality of the signal is ultimately limited by
the analogue performance of the converter used, not by the data format. Grimm
Audio strives to attain the best audio performance possible. The primary recipe is
to keep the signal path simple, resulting in a discrete-circuit continuous time archi-
tecture. This design was shown to deliver its best at 1 bit and 2.8224MHz sampling
rate. A substantially higher sampling rate would introduce settling time problems,
resulting in noise modulation artefacts. More bits would introduce linearity prob-
lems and yet another breed of modulation artefacts. This strategy has paid off in
unprecedented measured and sonic performance. For SACD mastering DSD is the
format of choice by default. And if your product will be released on CD (with 22 kHz
brickwall filtering) the supposed benefit of lower HF noise by using a higher sample
rate is entirely lost while the performance loss inside the 20kHz range, incurred by
optimising for out-band noise, is maintained.
While DSD is the format of choice for high quality recording and SACD mastering,
digital editing is performed with PCM audio. This because every change thatʼs made
to the DSD audio stream will lead to a wider word lenght then 1 bit. Since a mul-
tibit signal at 2.8224 MHz has a data rate thatʼs too high for practical use, DSD is
converted to a lower rate PCM format before editing. When Philips engineers were
building DSD editing tools the design criterion was thus to find a PCM format that
would not detract from the sonic capabilities of DSD. It was found that it was pos-
sible to convert a DSD signal to 352.8kHz/32 bit and back without incurring any
audible quality loss, as long as good care was taken with the filtering and remodu-
lation stages. Later on this format was called ʻDXDʼ. Conversion of DSD to DXD is
performed ʻon the flyʼ in certain DAWʼs.

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One could ask if it makes sense to record DSD format audio, when it will be edited
in PCM anyway. The answer depends on how your recording and editing sessions
are structured. Certainly for recordings made on stand-alone recorders, the use
of DSD as a storage format is warranted. Practice so far shows that DSD is at least
as sonically transparent as 192kHz/24 bit and better than 96kHz/24bit. However,
one channel of DSD takes up only 2.8Mbit/s, whereas one channel of 192kHz/24bit
takes up 4.6Mbit/s. Given that the AD1 puts out DSD data anyway, itʼs most eco-
nomical to store the audio in this format. Converting to PCM during recording
would only increase the data rate without any added benefit. The conversion to PCM
is best left to the Grimm Audio DD1 or the DAW when the recording is loaded.
When mastering an SACD, the final stage is a 1-bit noise shaper. Some people
worry over running a signal through a noise shaper twice. There are certainly prob-
lems (accumulation of HF noise) to be expected from applying several stages of
deltasigma modulation to an audio signal. Twice is not a problem, five or six times
is another matter. This means that using a deltasigma A/D in the front and a final
digital remodulator at the back is not going to cause any trouble. This is espe-
cially so considering the particular choice of modulator used in the AD1. For one,
as a continuous-time design it outputs slightly different data compared to a digital
modulator, meaning youʼre not stacking two identical processes. For another, its
outband noise characteristic is about the most gentle one found in DSD converters
anywhere, largely owing to the lack of coefficient rounding. The HF noise floor of
the digital remodulator is therefore always going to dominate the end result.
DSD maximum levels and HF noise
A topic that has caused quite a bit of confusion is the max level of a DSD stream.
The absolute signal level of a DSD signal is expressed as modulation index. A 100%
modulation index means all output samples are “1”, -100% means all output sam-
ples are “0”. When no signal is present, modulation index is 0% so on average half
of the output samples are “1”, the other half “0”. Practical analogue 1-bit modula-
tors produce negligible distortion when used below 50% peak modulation index. It
is therefore common practice to design the decimation filters in 1-bit based PCM
converters to output 0dBFS when the modulation index of the 1-bit modulator
output is 50%. This practice has become enshrined in the Scarlet Book standard,
where the 0dB reference level for DSD signals has been set to 50% peak modula-
tion index. The standard strongly recommends that the CD layer of hybrid discs be
derived from the 2-channel SACD layer with 0dBFS = 0dBDSD. All SACD players are
designed such that the signal levels in DSD and PCM modes match when this con-
vention is followed.
This does not mean, however, that the deltasigma modulator in DSD A/D convert-
ers falls apart above 50% modulation index, far from it. The AD1, for instance will
provide acceptable performance for signal levels up to +1.8dBDSD. Above this
level, modulator overload occurs. Using this margin to boost oneʼs loudness level

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by 1.8dB is not a good idea though. In order to get the best commercial SNR spec,
the D/A converters in most CD/DVD/SACD players max out at 0dBFS and hence
0dBDSD. Feeding them DSD signals modulated above 0dBDSD will cause analogue
overload in the filters, digital overload in the preprocessing or both. Therefore,
playing the Loudness Race game by modulating above 0dBDSD is liable to result in
unplayable discs.
The level confusion is further compounded by the peak level spec set forth in the
Scarlet Book. The Scarlet Book spec defines maximum allowable peak modulation
in terms of a running flat average of DSD data bits. A pressing plant will refuse
an SACD master if out of any consecutive 28 samples more than 24 or less than
4 are “1”. In modulation index terms this corresponds to ±71.4% or +3.10dBDSD.
In keeping with the Scarlet Book standard, DSD DAWs sport a peak reading meter
based on a 28-sample average. This has led to the belief that an SACD can be made
to play 3.1dB louder than a CD. This is quite incorrect, because a 28-sample un-
weighted average is a very shoddy low-pass filter and includes a very large amount
of shaped HF noise from the modulation process. A typical 1-bit modulator will
produce a “+3.1dB” reading on a 28-sample averaged level meter when the input
level is around +1.5dB. By the same token, maximum modulation level specs given
by several converter manufacturers are also misleading, because they state the 28-
sample average reading at the 1-bit output, not the corresponding input level.
A problem related with HF noise is encountered when mixing tracks, recorded in
DSD. Some people found there was hardly any HF headroom. Watching the HF me-
ters in their DAW showed various amounts of noise when comparing AD converters
but no AD provided low enough HF noise to facilitate normal mixing. Indeed there
is quite some variation in the amount of HF noise put out by DSD A/D convert-
ers. Most converters use a front-end running at a different sample rate or word
length and use a digital modulator to convert this to a signal compatible with the
DSD spec. Quite often these digital modulators are designed for the lowest possible
noise floor. Tested using a digitally generated signals, better than -130dB in-band
noise is common. This is quite suboptimal because only the signal-to-noise ratio
of the analogue front-end needs to be accommodated, while the improved “virtual”
noise level comes at the expense of greatly increased HF noise levels. A similar ef-
fect is encountered in the 1-bit remodulation stages in DSD DAWs.
The main reason for the mixing problem however is not all DSD DAWs use the best
processing filters. During the development of DXD for editing of DSD signals, much
effort went into designing filters with optimum cut-off and slope that were de-
monstrably transparent in listening tests while providing enough HF attenuation to
deliver precisely the processing margin required by practical processing needs.
If you find your DSD production system does not have the headroom needed for
mixing large numbers of channels with substantial gain, this may be an indication
of the DAW and/or the ADC not implementing the best possible filters and remodu-
lation stages. A Grimm Audio DD1 format converter will solve this issue.

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4. Specifications
Discretely build continuous-time 6th order sigma delta modulator running at 64
x 44,1 kHz or 2.822 MS/s (DSD). As shown in the block diagram, only four resis-
tors separate the audio signal from the feedback DAC. Everything else is within the
feedback loop.
The clock PLL is a hybrid analog / digital design, based on a custom ultra-low jitter
crystal oscillator. It features a ʻtightʼ mode with attenuated jitter rejection at low
frequencies to comply to the SDIF3 standard when necessary.
The power supply has CLC filtering after rectification to provide a relatively clean DC
voltage for internal distribution. Each channel has local shunt regulators featuring
120 dB power supply rejection and a high impedance supply path. Thus all varia-
tions in load current are kept local to the circuit. The power buss and ground carry
only DC current.
Specifications
Frequency response ±3 dB: 0 Hz – 55 kHz.
THD at full signal: -127 dB (both balanced and unbalanced).
Noise (20 kHz bandwidth): -116 dB.
Idle mode HF noise: 9 dB below Scarlet Book appendix E&F.
6 order, continuous time
loop integrator
th
Summing
network
H(s)
1-bit D/A converter
Comparator
D Q Out
Latch
Clock in (2.8224MHz)
Output spectrum with full scale input.
10 20k20 50 100 200 500 1k 2k 5k 10k
Frequency (Hz)
1p
100f
10f
1f
100a
1p
100f
10f
1f
0.5
Uncorrelated Jitter (s/Hz )
Correlated Jitter (s)
Jitter spectrum at converter stage.

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Input sensitivity: 18 dBu for 0 DSD. Equal performance on balanced and unbalanced
sources.
Input impedance: 10 kOhm balanced, 5 kOhm unbalanced.
Data outputs SDIF3 compliant.
Output impedance = 60 Ohm.
Word clock input Zin = internally selectable HiZ or 75 Ohm (default HiZ).
Word clock input threshold for ʻ1ʼ level > 0.5 Vpp.
Word clock output Zout = 75 Ohm.
Latency word clock out - data out: 3 ns.
Latency word clock in - word clock out, Tight mode: max ±20 ns depending on
input clock jitter. Ultra mode adjusted to less than 50 ns, but may be larger due to
input clock jitter.
Internal intrinsic clock jitter 2,1 ps RMS (above 10 Hz) at converter stage.
PLL performance (slave mode):
Ultra mode 90 dB attenuation @ 10 Hz, improving at 60 dB/dec above that.
Tight mode 36 dB attenuation @ 100 Hz, improving at 60 dB/dec above that.
Maximum ambient temperature for operation: 40 degrees Celsius.
The unit shall be mounted in a 19” rack keeping at least 1U empty space above and
below.
Life expectancy power supply electrolytics > 45.000 hours if case is installed ac-
cording to our requirements
Weight: 15 kg
Dimensions: 440 x 388 x 85 mm.
Power consumption 8 channel box: 100 W.
Wood type of front: Mahogany.
Grimm Audio contact information
Grimm Audio CV
Kanaaldijk-Zuid 11
5611 VA Eindhoven
The Netherlands
[phone]
Email: [email protected]
Website: http://www.grimmaudio.com

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5. Grimm Audio Limited Warranty
Grimm Audio CV (“Grimm Audio”) warrants this product to be free of defects in
material and workmanship for a period of one (1) year for parts and for a period of
one (1) year for labor from the date of original purchase. This warranty is enforcable
only by the original retail purchaser and cannot be transferred or assigned.
During the warranty period Grimm Audio shall, at its sole and absolute option,
either repair or replace free of charge any product that proves to be defective on
inspection by Grimm Audio or its authorized service representative. In all cases
disputes concerning this warranty shall be resolved as prescribed by law. To obtain
warranty service, the purchaser must first call or write Grimm Audio at the address
and telephone number printed below to obtain instructions where to send the unit
for service. All enquiries must be accompanied by a description of the problem. All
authorized returns must be sent to Grimm Audio or an authorized Grimm Audio
repair facility postage prepaid, insured and properly packaged. Proof of purchase
must be presented in the form of a bill of sale or some other positive proof that the
product is within the warranty period. Grimm Audio reserves the right to update
any unit returned for repair. Grimm Audio reserves the right to change or improve
design of the product at any time without prior notice.
This warranty does not cover claims for damage due to abuse, neglect, alteration or
attempted repair by unauthorized personnel, and is limited to failures arising dur-
ing normal use that are due to defects in material or workmanship in the product.
In no event will Grimm Audio be liable for incidental, consequential, indirect or
other damages resulting from the breach of any express or implied warranty, in-
cluding, among other things, damage to property, damage based on inconvenience
or on loss of use of the product, and, to the extent permitted by law, damages for
personal injury.
© 2006, Grimm Audio CV. All rights reserved
Reproduction in whole or in part is prohibited.
Specifications subject to change without notice.
AD1man01, 2/15/06