Edison Revisited
by Scott Cannon
Advisors:
Dr. Jonathan Berger and Dr. Julius Smith
Stanford Electrical Engineering
2002 Summer REU Program
Scott Cannon- 2002 EE REU Program
Edison Revisited
Background
The first phonograph was developed in 1877 as a
result of Thomas Edison's research on two other
inventions, the telegraph and the telephone.
By 1908, the Edison
Phonograph could play four
minute recordings from 2
inch diameter wax cylinders
which rotated at 160 rpm.
The machines were handcranked, and used for music
recording and business
dictation purposes.
Scott Cannon- 2002 EE REU Program
Edison Revisited
Background
A collection of more
than 1500 original
cylinder recordings,
and two fully functional
phonographs were
recently donated
anonymously to
Stanford University for
use as an educational
tool, and to be enjoyed
by anyone via the
internet.
Scott Cannon- 2002 EE REU Program
Photo: an early recording session,
circa 1900
Edison Revisited
Goals
The Edison Project focused on
achieving two primary goals:
1) Digital
encoding and preservation:
To develop an efficient, high-fidelity
means of capturing, processing,
distributing, and preserving a
collection of more than 1500 original
Edison Cylinder recordings.
2) Audio Restoration:
To research and design high-quality
algorithms for removing distortion
artifacts that are inherent to 90 year
old recordings.
Scott Cannon- 2002 EE REU Program
Edison Revisited
Part I: Method
In Part I, research was focused to determine the best
means of capturing and processing the audio from the
phonograph. Every step of the signal chain was
examined and constructed to maintain the highest fidelity.
Focus of Part II
Phonograph
Microphone
AD Conversion
Computer
Processing
The Internet
-The signal begins
with an original handcranked Edison
phonograph, nearly
100 years old.
-In addition, our
research also
explored the use of
professional cylinder
players using today’s
technology.
- Over a dozen
microphones of
various pickup
patterns were
auditioned in
different
locations around
the phonograph.
-All capture was
done at 44.1 kHz,
and 16 bit (CD
quality)
-Selected
recordings were
captured using 24
bit encoding at 48
kHz, for
-A laptop was
used for
flexibility
-Digital editing
was completed
with Wavelab,
Matlab,
SoundForge,
and Protools
software.
Each recording
received a mix of:
Recordings were
converted to .MP3
format for internet
distribution, and
cataloged in a
detailed database
at CCRMA.
Scott Cannon- 2002 EE REU Program
-Noise reduction
-Click removal
-Equalization
-Pitch Correction
-Adjustments for
eccentricity
-Dynamic range
compression
Edison Revisited
Part I: Results
A wide array of tests examined each component in the signal
chain to create the best combination of equipment and tools.
Frequency Response
For example, it was discovered, that a
stereo microphone configuration placed
1.5 meters from the phonograph captured
5 dB less noise (around 1730 Hz) than a
high-proximity microphone at 10 cm.
Mic 10cm away
Mic 1.5 meters away
Scott Cannon- 2002 EE REU Program
Noisy Frequencies
While this
configuration helps
to mitigate noise, the
stereo recordings felt
more distant to some
listeners, who
preferred a close
microphone with
acoustic dampening.
Edison Revisited
Part I: Results
Frequency Content of Captured Sound
(se
c)
Amplitude
(dB)
Tim
e
Analysis showed that the
phonograph produced no
significant content above 4 kHz.
In addition, content below 80 Hz
was negligible. Thus data
compression algorithms and a
bandpass filter were selected to
deliver only the relevant content
to the listener, resulting in a
smaller file size for faster
distribution over the web.
Frequency (Hz)
The final system integrated the results of these and many
other measurements at all points in the signal chain to
capture the highest quality sound possible.
Scott Cannon- 2002 EE REU Program
Edison Revisited
Part II: Method
Part II of this research project
aimed to develop a novel method
to reduce the “pops” and “clicks”
(very brief distortions caused by
dirt and scratches) that are
inherent to phonograph
recordings.
These signal distortions are eliminated through
two primary processing steps:
1) Detection of the signal distortion.
2) Replacement of the distorted sound with an
interpolated estimation.
Scott Cannon- 2002 EE REU Program
Edison Revisited
Part II: Results
Matlab was used to
create algorithms that
effectively detect
substantial distortions,
and splice good data
from surrounding
areas such that there
are no signal
discontinuities in the
new waveform.
Original, distorted waveform
Amplitude (db)
Distortion detected and removed
The results sound
very good!
Scott Cannon- 2002 EE REU Program
New, interpolated waveform
Time (ms)
Problem Area
Edison Revisited
Discussion
While our algorithms for removing distortion
performed well for distinct artifacts in the
waveform, the ability to remove more subtle
forms of audible distortion proved elusive with
these methods.
Future research will attempt to develop similar
methods based on minimum variance estimation
under various modeling assumptions to more
effectively “clean up” old analog recordings.
Scott Cannon- 2002 EE REU Program
Edison Revisited
Conclusion
This research project accomplished two goals:
Digital encoding and preservation:
An efficient, high-fidelity means of capturing,
processing, distributing, and preserving a
collection of more than 500 original Edison
cylinders was developed. Files are posted at
http://ccrma-www.stanford.edu/groups/edison/
Audio Restoration:
A method for removing signal distortion was
created. A foundation has been built on
which to develop more robust algorithms.
Scott Cannon- 2002 EE REU Program
Edison Revisited
References
Godsill, Simon J. and Rayner, Peter J.W. Digital Audio
Restoration. 1998. Springer, London.
Oppenheim, Alan V. and Willsky, Alan S. Signals and
Systems, Second Edition. 1997. Prentice Hall.
Lockhart, G. B. and Goodman, D. J. Reconstruction of
missing speech packets by waveform substitution. In:
Signal Processing 3: Theories and Applications. 1986.
Garbit, Frederick J. The Phonograph and its Inventor,
Thomas Alva Edison. 1994. Gunn, Boston.
Scott Cannon- 2002 EE REU Program
Edison Revisited