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Audio Authenticity Analysis
Audio Authenticity Analysis
When the authenticity or integrity of a forensic audio
recording is in question, our analysts conduct detailed forensic analysis to
determine if material has been deleted, added, altered or changed in audio analog or
audio digital recordings.
 All analog tape recorders have at least two heads, an
erase head and a record/play head. The tape first travels past the erase
head, which erases any existing recording before it reaches the record/play
head. When the record mode is engaged, a magnetic impression or “signature”
is left on the tape by both the erase head and the record head. As the tape
travels past the record head, it erases the signature left by the erase head.
Consequently only the record head signature is left. When the tape is
stopped, a signature of both the erase head and the record head is left. Our
forensic audio software system is able to view the graphical display waveform of
the material contained on the tape. The signatures are visible on the waveform,
and may be both seen and heard when played on the computer. When stop, start,
pause or editing occurs a signature is permanently left on the recording. These
signatures can be viewed and printed for comparison. If suspect signatures
are found during analysis, the original recording device will be
requested in order to conduct comparison testing for the purpose of making a
conclusive determination.
Signs of Altering or Editing Audio Recordings (Types of signatures):
- Stop/Start: Tape recorder in record mode is stopped,
and then the record mode is re-engaged with no intervening tape transport
function having been engaged. These are often the record events of most
concern to the forensic audio expert.
- Stop/Advance/Start: Record mode is stopped, then the
tape is advanced, then record mode is engaged again.
- Stop/Rewind/Start: Record mode is stopped, then
record mode is engaged again. If the tape has been rewound to a point just
prior to the position of the “stop” signature, this will effectively eliminate
(or erase) the “stop” signature, leaving what appears to be only a “start”
signature at this point on the tape.
- Start/No-Stop: Record mode is engaged, and then tape
runs out and reaches the leader while recording is in process. (Microcassettes
have no leaders.)
- No-Start/Stop: When record mode is engaged on the
plastic leader it is not recorded, and then the record mode is disengaged
later on the tape.
- Pause: Recorder is stopped by pausing, and then
re-engaged by de-pausing.
- Voice Activated Start/Record/Stop: Voice activation
circuitry is used to engage, then disengage, record mode.
Though stop, pause and start signatures are recognizable,
different recorders have unique characteristics.
Digital Editing: An audio professional can delete or
alter material from a tape by use of digital audio software in such a way that
the average person will usually not be able to detect it. Only through analysis
by a forensic expert can such determination be made.
Edit Tracker: Stutchman Forensic Lab utilizes Edit
Tracker from the Center for Speech Technology in Russia. Edit Tracker is a
sophisticated software package specifically engineered to detect prior
digitization, breaks in phase continuity, sudden change background noise and
other indicators of analog or digital editing.
Terms and Definitions for Understanding Analysis
Analog Recording: An analog recording is one that is
made using conventional magnetic tape. This includes standard audiotape and
microcassette recordings.
Digital Recording: A digital recording does not use
magnetic tape. It records the information using configurations of 0’s and 1’s.
The information that comprises the recording is stored on digital media,
consisting of a computer chip, digital media card or computer sound file.
Compression: Many digital recorders use compression. In
a lossy compression scheme, as the name implies, some of the original
information is discarded when it is compressed. Therefore, it is impossible to
produce an exact replica of the original audio signal when the audio is played.
There are many different schemes of lossy compression available. These schemes
generally provide varying compression ratios. The most popular of these, the
MPEG, or MP3 format, is commonly employed with compression ratios of up to ten
to one. All lossy compression schemes add artifacts to the compressed audio as
well as decreased audio clarity. Artifacts are small imperfections created by
the loss of the actual audio data.
WAV File Format: Standard digital audio file format for
storing waveform data; often used to save CD-quality audio. WAV (WAVE) files are
similar to .AIF files used by Apple computers, but they use a more complex
format and are more common on Windows-based systems.
Waveform display: When a recording is fed onto computer
using forensic audio software or audio editing software, the recording is viewed
in terms of a graphical display called the waveform. The waveform display
reflects graphically the relationship between the time and amplitude of recorded
sounds and allows the identification and comparison of record events on evidence
and test recordings.
Magnetic Signature: When a record event occurs on an
analog recording a magnetic impression, known as a signature, is permanently
placed on the tape recording by the record head and the erase head. These
signatures have generic similarities and individual characteristics. A
particular tape recorder can be identified or eliminated by analysis of the
magnetic signatures. These signatures identify when a recorder was started,
stopped, re-started or paused.
Record Event: A record event is an occurrence that
initiates, interrupts or stops a recording process.
Anomaly: An abnormality in a recording, which is of an
undetermined origin.
Discontinuity: An event that interrupts the continuous
flow of recording. It can occur either in the original recording, by stopping or
pausing the recording, or by post recording editing.
Edit: Editing is a process of altering the content of a
recording. There are a variety of methods by which a recording can be edited.
Edits can be done during the recording process or after the recording is
completed.
Methods Used to Detect Alterations of Audio Tapes/Recordings
Physical Inspection: Physical inspection was done to
determine the condition of the tape and to inspect for any damage that would
affect how it functions.
Critical Listening: Critical listening is an aural
evaluation of the audio recording, which provides considerable direction to the
examiner in locating areas requiring specific instrumental or physical
inspection.
Waveform Analysis: When a recording is fed onto
computer using forensic audio software or audio editing software, the recording
is viewed in terms of a graphical display called the waveform. The waveform
display reflects graphically the relationship between the time and amplitude of
recorded sounds and allows the identification and comparison of record events on
evidence and test tapes. When a record event occurs such as a start, stop,
stop/re-start or pause on a magnetic analog tape, a distinctive mark or
signature is placed on the tape. When waveform analysis is conducted, these
signatures can be seen and in most cases, heard.
Spectrographic Analysis: A sound spectrograph displays
the recorded material in time, frequency, and amplitude. Its distinctive display
is used to further study the effects of record events, etc. Any gap in the audio
signal as well as signatures can be examined on the spectrograph.
Magnetic Development: When the tape recorder heads
touch or leave the magnetic recording tape, they leave a signature like a
fingerprint. That signature is indigenous to the tape recorder. The process of
magnetic development allows for these signatures to be examined under
microscopic magnification by applying a non-destructive Freon-based
ionized-particle solution.
Edit Tracker: As indicated above, Edit Tracker is a
sophisticated software package specifically engineered to detect prior
digitization, breaks in phase continuity, sudden change background noise and
other indicators of analog or digital editing.
As experienced expert analysts, our highly trained and
qualified forensics team uses top of the line hardware and software technology to
carefully handle and thoroughly analyze your evidence audio, video, and
photographic media. We can isolate,
separate, enhance, and authenticate all relevant aspects of audio and video recordings in
order to produce
expert evidence backed by many years of master experience. As
an
expert witness in the courtroom, our testimony from the witness stand will
contain provable facts and relevant
demonstrative evidence that can often make or break a
case.
Let us serve you.
Contact Us at
(800)
799-0828
Relevant areas of Audio Authenticity Analysis include
Audio
Forensics, Audio Enhancement,
Voice Identification,
Audio Video,
Voice
Comparison,
Voice ID,
Audio Authentication and
Authenticity Analysis,
Audio Expert,
Audio Analysis for Timing and Sequence of Events,
Expert Witness,
Tape
Analysis,
Audio Acoustical Analysis and Sound Measurement,
Forensic Tape Analysis,
Audio,
Forensic Transcription
Services,
Voice Recognition,
Gun Shots
and
Gun
Shot Analysis.
We provide services nationwide across the United States of
America in cities such as Chicago, Los Angeles, San Francisco, Anchorage,
Seattle, San Diego, Portland, Honolulu, New York, Denver, Tampa, and many others.
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