Reveal Audio: Forensic Audio Enhancement Services
Reveal Audio Services has been helping individuals, private investigators, attorneys, and law enforcement for the past twelve years with their forensic audio needs. J David Leonard, owner of Reveal Audio Services, has been a recording engineer for over 25 years and has broad experience in both digital and analog editing and signal processing.
Member of AES (Audio Engineering Society)
Associate member of GAPPI (Georgia Association of Professional Private Investigators)
Member ACFEI (American College of Forensic Examiners, Int'l)
Certified Forensic Consultant
Contributed the "Audio Recordings" portion to the book, "Key Terms and Concepts for Investigation" by John J. Fay,
Reveal Audio Services is able to provide clients with the following services:
- Audio noise reduction
- Reduction of hum and other steady tone interferences
- Minimization of impulse noise interference
- Correction of volume gain imbalances
- Distortion reduction
- Single voice extraction from multiple speakers or background music
- Tonal balance and correction of speech
- Forensic transcription
- Spectrograhic analysis
- Expert reports
- Expert testimony
I strive to deliver a quick turnaround to you, usually within 48 hours.
Is your sound-recording “at a loss for words?”
Using state of the art computer technology and accepted scientific methods, Reveal Audio Services is able to reduce or remove a variety of unwanted background noises in order to improve the intelligibility of poorly recorded audio.
NOISE REMOVAL: REASONS FOR POOR QUALITY RECORDINGS
The interactive demonstration on this page has samples of "real world" before and after audio enhancements for a number of different noise situations.
Due to the nature of this type of recording, honestly, some things just can’t be helped.
Many recordings are made with a small handheld microcassette or digital voice recorder concealed in a shirt pocket or a purse. As a result, the sound appears muffled and the sibilant sounds of speech (esses, effs, etc) are hard to hear. Another side effect is that the recording level of the person speaking is much louder than the person being recorded due to the relative distance to the microphone. This causes another problem. The microphone picks up the sound reflections coming off the walls, floor and ceiling, blurring the speech.
Device settings also contribute to poor fidelity. Microcassette devices only have so much tape to record with. Digital devices only have so much memory. The length of recording time available is inversely related to the recording quality you select. The better the quality, the less time is available. With microcassettes, this is determined by the speed of the tape. With digital devices this is the sampling bitrate. Again, the first thing to go is the high end sibilant sounds; and with digital devices other artifacts appear such as phasing (that “underwater” sound). Also, let’s not forget distortion caused by incorrectly set record levels or faulty automatic level compensating circuitry.
Power sources sometimes cause interference. If the recorder is placed near a power source with a strong transformer, the electrical hum can often be as loud as the voice signal. In cheaper microcassette recorders, the noise of the motors that drive the cassette hubs can be picked up by the recording heads and heard on the tape.
Other external devices can leave their mark as well. For instance, “smart” phones generate strong pulses that can be picked up by recorders located many feet away. Some medical equipment generate loud tones as well. Air conditioners create full-spectrum noise that is difficult to separate from low speech signal. Televisions and radios are particularly tough when it comes to noise removal because much of the broadcast contains actors’ and commentators’ dialog.
The location itself can pose challenges for audio cleanup. For example, the traffic that speeds along a highway makes loud swooshes as the cars pass by. If a recording is made over dinner in a restaurant, there are other conversations going on simultaneously along with ambient music and the general noise associated with food service.
AUDIO ENHANCEMENT: TECHNOLOGY TO THE RESCUE
Reveal Audio Services uses specialized software that was developed just for the purposes of noise removal - reducing the noises that interfere with and mask speech signals. This is not the kind of software you find in a music recording studio. Music editing and audio restoration deals with the fine points of noise reduction using gentle curves and subtle processes to preserve as much of the musical tones as possible. The standard music tools just don’t go far enough for forensic audio work.
The software I use is adaptive by design, meaning that as the interfering noises change, the software algorithm “learns” them and adapts in a matter of milliseconds. Interfering beeps and pulses can be diminished greatly. 60-cycle hum can be nearly eliminated. Traffic “swooshes” can be minimalized.
The range of settings available is more powerful as well. For instance, a typical music equalizer may have 6 bands to work with, with a range of +/- 18 decibels. For forensic audio enhancement work, I am using an equalizer with 4,096 bands and a range of +24 to -96 decibels.
This is not Hollywood CSI magic that appears at the touch of a button. This is the real world and the process is not that simple. It requires a different listening mind-set, a tremendous amount of audio knowledge and expert proficiency with the software to achieve results that range from an acceptable improvement to jaw-dropping clarity.
AUDIO SERVICES: PRESERVING AUDIO QUALITY
Knowing that I will be getting a difficult recording for audio cleanup in the first place, I try to preserve the quality of the recording as much as possible.
The best quality digital format is “uncompressed PCM”, such as a WAV or AIF file. These are very large (10 MB/minute for a stereo file) and as a result are almost never used as the format for a digital voice recorder. These recorders rely on clever algorithms to reduce the size of the file by REMOVING frequencies that it calculates won’t be heard. So one way to see it is that you can record 10 times longer; another is that you are now missing 90 percent of your information. Editing one of these files is like blowing up the picture you took with your cellphone to the size of a billboard. While I can’t get back that missing 90 percent, I can at least ensure that the recording isn’t further degraded during the editing process.
If the recording is analog (microcassette or cassette), it is recommended that safety recording tabs be knocked out to prevent any unintentional recording on the tape. The tape is played once in order to transfer it to a hard drive as a WAV file using state of the art analog-to-digital convertors at CD-quality sampling rates. This is where the real work will be done.
If it is a digital recording, many times the device has a USB connection that, when connected with a computer, allows it to be read like any other drive. The files on the device can be easily copied to a hard drive in order to be sent to me. Other devices have a proprietary software application that is used to convert from the native format to a more widely used format. In those cases, the original device is needed to make the transfer and then convert it using the highest quality that the conversion software can give. From there it will be upsampled to CD quality before beginning the audio enhancement processes.
If the recording is delivered to me as data files on a flash drive or CD/DVD, I will first check to make sure that the format of the files is CD quality. If not, they will be converted to 16-bit/44.1kz WAV files.
If the audio is part of a DVD or streaming video, the audio will be separated from the video, and after audio cleanup, recombined back with the video.
FORENSIC AUDIO: LEGALITY
Georgia is a “one party” state. This means that the state of Georgia does not prohibit a person who is a party to a conversation from recording it, and does not prohibit recording if one party to the conversation has given prior consent. In other words, it is OK if two people are having a conversation and one of them is recording it. The recording can be presented in a court of law.
On the other hand, a recording made with a hidden device under the bed or the car seat with only one of the parties present may be enlightening, but is not admissable.
It is important to be able to reference any edited recording with the original in order to prove that the words on the recording have not been altered – only that the intelligibility has been improved. I make sure to provide you with the original version of the recording in addition to the audio enhanced version. In cases where only parts of the original recording are extracted and processed, they are referenced by their time location and duration in the original.
Concerning video, it is illegal to use a hidden video camera "without the consent of all persons observed, to observe, photograph, or record the activities of another which occur in any private place and out of public view."
AUDIO ENHANCEMENT: COST
Every audio cleanup case is different, and I base my fees on the estimated time involved. Based on a description over the phone, I’m usually able to give a reliable quote within a 20% range based on the length of the recording and the type of interference it contains. Sometimes, however, there is a problem with the audio that only shows up once the recording is in hand and the work is in progress. In such a case, I will communicate with you right away as to the nature of the problem and the options for dealing with it.