T+A Elektroakustik SADV 1245 R Page 48 Operating Instructions Manual Download

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Technical description

OVERSAMPLING

The audio data on CDs and DVDs is stored at a sampling
rate  of  44.1  or  48 kHz  -  i. e.  for  each  second  of  music
44.100  or  48.000  sampled  values  are  available  for  each
channel.  In  the

SADV 1245 R

the audio data read from

the  DVD  or  CD  is  „multiplied“  to  a  higher  sampling  rate
(384 kHz) before it is converted back into analogue music
signals. This process delivers a significantly better, more
finely  graduated  signal  to  the  converter,  which  can  then
be  converted  with  correspondingly  higher  precision.  The
raised  sampling  rate  is  a  calculating  process  for  which
there  are  many  different  mathematical  methods.  In
almost  all  digital  audio  devices  which  exploit  the
advantages  of  increased  digital  sampling  rate  a  process
known  as  a  FIR  (Finite  Impulse  Response)  filter  is
employed  for  this  purpose.  At



we have been

carrying  out  research  for  more  than  ten  years,  aimed  at
improving  the  oversampling  process,  because  the
standard FIR method has one drawback to set against its
indisputable  advantages:  it  adds  small  pre-  and  post-
echoes to the music signals. At



we have developed

mathematical  processes  (known  as  Bezier  polynomial
interpolators)  which  do  not  share  this  disadvantage.  For
this  reason  they  should  sound  better  and  more  natural
than  the  usual  standard  process.  Since  the  calculating
procedure  employed  by  us  is  con-siderably  more
complex  than  the  standard  method,  the

SADV 1245 R

features  a  high-performance  digital  signal  processor
(DSP)  which  carries  out  the  over-sampling  process  with
immense  precision  (56 bit)  using  special  algorithms
developed by



The  freely  programmable  DSP  which  we  use  is  capable
of  carrying  out  the  oversampling  process  using  any
method  of  calculation.  For  this  reason  we  have  im-
plemented  two  slightly  modified  Bezier  processes
(OVS 2)  in  the

SADV 1245 R

in addition to the pure

Bezier process (OVS 3), together with two variants of the
standard  process  (standard  OVS  FIR  filter  and  OVS 1).
For  more  information  on  the  different  processes  please
refer  to  the  next  section.  You  can  switch  between  the
different algorithms using the FILTER button, and decide
for your-self which of the filters you prefer.

Standard OVS FIR filter

The long FIR filter  is  the  standard oversampling process
in  digital  technology,  offering  extremely  linear  frequency
response,  very  high  damping,  linear  phase  charac-
teristics and constant group delays. The disadvantage is
the pre- and  post-echoes  which  are added  to  the signal.
These  „time  range  errors“  tend  to  affect  the  music
signal’s dynamics, precision and naturalness, and reduce
spatial orientation.

Frequency response and transient characteristics of
the long FIR filter

OVS 1

(short

FIR

filter)

Shortening the filter (lower coefficient) reduces the time
range errors, albeit combined with a slight loss of linearity
in the frequency range and damping per-formance.

Frequency response and transient characteristics of
the short FIR filter

OVS 2

(

Bezier

interpolator plus

IIR

filter)

In  this  process  an  ideal  Bezier  interpolator  is  combined
with  what  is  known  as  an  IIR  filter.  This  eliminates  the
problematic  pre-echo  of  the  FIR  method.  This  process
produces highly „analogue“ system characteristics, with a
sound quality and measured performance similar to those
of good analogue disc players.

Frequency response and transient characteristics of
the Bezier interpolator plus IIR filter

OVS 3

(pure

Bezier

interpolator)

This  process  delivers  a  perfect  reconstruction  of  the
original music signal. It exhibits no pre- or post-echoes of
any kind, and does not add coloration or timing errors to
the  original  signal.  In  sonic  terms  this  method  offers  an
impressive  blend  of  naturalness,  good  dynamics  and
accuracy. This is our preferred process due to its advan-
tages  in  respect  of  sound,  and  is  the  basic  (default)
setting of the

SADV 1245 R

Frequency response and transient characteristics of
the Bezier interpolator

Note:

For optimum performance of the



oversampling

algorithms please select

CD-Upsample

OFF

in the menu

PREFERENCES / SOUND

We suggest to use this setting at all times.