Transcript based on one copy of the archive recording

METHODS FOR DETECTION AND
REMOVAL OF PARASITIC FREQUENCY
MODULATION IN AUDIO RECORDINGS
CZYZEWSKI A., MAZIEWSKI P., DZIUBINSKI M., KACZMAREK A.,
KULESZA M., CIARKOWSKI A. & KOSTEK B.
Multimedia Systems Department
Gdańsk University of Technology (GUT)
Poland
Schedule
 Wow
& flutter – basic facts and
definitions
 Methods of estimating parasitic
frequency modulation in audio
 Our algorithms and software
 Sound examples
 Conclusions
Wow & flutter – parasite effects
-
The wow & flutter defects can be found in:
- Recordings, especially archival
on magnetic and optical sound tapes
- Those defects can occur during:
- sound recording
- copying procedure
-
The main sources of those defects are:
- irregular velocity of the sound carrier movement
- mechanical tape damages
-
-
Parasite wow (flutter) distortions can be
characterised as an undesirable changes of all
sound frequency components
Eliminating them should help to understand the content
of some still unresolved archival speech recordings
Wow & Flutter problem
Drift
fmod < 0.5Hz
Wow
fmod  < 0.5 – 6Hz >
Flutter
fmod  < 6Hz – 100Hz >
Frequency-modulation noise
fmod > 100Hz
Standards related with wow &
flutter
Examples of well known standards :

Magnetic Tape Recording and Reproducing (Reel-to-Reel)
NAB Standard 1965 (National Association of Broadcasters)
Messgerate fur Frequenzschwankungen bei
Schallspeichergeraten (Measuring Equipment for Frequency
Variations in Sound Recording Equipment)

DIN 1966

Measurement of Wow and Flutter in Recording
Equipment and in Sound Reproduction
CCIR Recommendation 1970

Method for Measurement of Weighted Peak Flutter of
Sound Recording and Reproducing Equipment
IEEE 1953 (1971)
AES 1982 (2003)
It is generally accepted that flutter should be less than 0.15% DIN weighted to be
inaudible. Measurement methods (2) are described in IEC 386, and a suitable test film
is available from the SMPTE (No. P35-FL).
Wow Restoration algorithms

The defect is difficult to estimate and to restore

We developed several algorithms for wow restoration
Preservation towards storage and
access. Standardised Practices for
Audiovisual Contents in Europe
FP6-IST-707336
PrestoSpace partnership
: INA
–
Coordinator
–
Project Steering Board
: BBC, RAI, INA, ORF, Joanneum Research (Austria), B&G (NL), Sheffield
University (GB)
–
Partners :
CTM Debrie, ACS, Media-Matters, CRCDG, Centrimage, Vectracom, SWR, Front Porch
Digital, Hi-STor, Houpert Digital Audio, LIMSI-CNRS, Snell&Wilcox, TI Partners, Universities…
–
Three partners to be identified in second phase of the project
–
External User Group
: 30+ considered archives.
Methods of the restoration of pitch
variation defects
based on comparison of the multiple copies of degraded
audio




time warping algorithms applied in time or
spectral domain (appropriate algorithm should
generate the correct time warping function or
pitch variation function).
adaptive filtering (estimation of time delay
(offset) between selected copies).
correlation methods (finding similarities based
on cross-correlation function).
statistical methods (maximum likelihood
estimation or true Bayesian estimation –
depending on knowing the priori information).
Methods of the restoration of
pitch variation defects
based on one copy of the archive recording
speech applications – lowpass filtering
followed by pattern matching.
 speech - cepstral analysis which reveals
information about the fundamental frequency.
 music or speech - application of methods
based on a knowledge of the shape of the
nonlinear function of audio distortion.
PVC = Pitch Variation Curve

Methods of the restoration of
pitch variation defects
based on one copy of the archive recording

multiple pitch tracking based on :
– McAulay and Quatieri representation (pitch tracking
through the use of multiple concurrent pitch
“tracks”)
– Analyzing high-frequency bias
– Analyzing recorded power-line hum (AC power
supply)


pitch tracking algorithms should generate the
correct pitch variation function (PVC)
based on pitch variation the restoration of the
signal can be done for example by resampling
it with a truncated sinc function.
Our algorithms…
presto8.exe (7)
Carrier feature analysis

Tracking power-line hum frequency
Hum is commonly found in archival recordings. Tracking
its frequency allows estimating the depth of wow effect.
Due to limitations of DFT methods in case of lowfrequency signals, the AR pseudospectrum estimation
method is used.

Tracking high-frequency bias
Assuming that a high frequency bias was recorded on the
magnetic tape it could serve as an ideal target for
parasite wow characteristic determining. This idea was
also exploited in the prepared software.
Wow Restoration Plugin
ORIGINAL
Wow
No Wow
RESTORED
Conclusions






MQ analysis can be effective in case of parasite frequency
modulation detection
Formant structure analysis can significantly improve
efficiency of the detection process
Precise wow tracking can be achieved based on a cepstrally
smoothed spectrum representation
Recorded power line hum provides a good basis for wow
tracking (similarly to high-frequency bias in magnetic
recordings)
Interactive procedures (parameters adjustment) leads to
more reliable results
It seems that an interactive approach employing an
algorithmic „toolbox” for wow&flutter restoration is the best
solution of this problem
Thank you
for your kind attention