Posts filed under ‘Forensic Audio’

Solved by forensic audio detection

Some TV crime scene investigation programs tend to be more fiction than reality for the sake of drama. But even if you disregard the drama, today’s audio evidence restoration possibilities are truly amazing.


What is audio restoration? It’s more than someone running your audio program through an equalizer (a glorified tone control with multiple frequencies). The process actually seeks to repair the sound. If you are faced with restoring audio evidence, here are some aspects in regard to the process to familiarize yourself with before speaking with a forensics audio engineer:

Audio Recording

Audio Recording

  • Decide exactly what sections of the evidence need to be restored.
  • Know the time length of the audio to be processed.
  • Identify the media format of the recording (example: micro or standard cassette).
  • Provide the original recording, if possible (copies introduce more noise).
  • Make sure the restoration process is non-destructive to the original recording.
  • Get an evaluation sample and listen to what can be done to improve your recording before you commit to having the whole recording processed.
  • Have the restored audio supplied in a trial-ready format.

There are many resources in a forensic audio engineer’s restoration toolbox: volume leveling, analogue and digital EQ, compression, expansion, scientific filters and advanced analysis software. Many projects require a combination of these be applied. Even projects that are less demanding or cost-sensitive may still benefit in the intelligibility aspect of the recording.

What can be restored? Conversations made on hand-held recorders, audio from video tape, phone conversations, and surveillance recordings. An experienced forensic audio engineer can repair, improve or eliminate unwanted noise and improve the intelligibility of a recording suffering from issues such as:

Get rid of the NOISE

Get rid of the NOISE

  • AC hum

  • HVAC units
  • Cameras
  • Generators
  • Motors
  • Noise from mechanical damage to the recording
  • Wireless microphone noise
  • Distortion caused by overload
  • Ambient room noise
  • Buzz
  • Fixed frequency noise
  • Clicks and pops
  • Crackle
  • Background noises

SoundWorks has over 25 years of experience in forensic audio and has restored hundreds of sound recordings. We also supply expert witness services and have testified in local, county, state and federal cases


March 18, 2009 at 8:10 pm Leave a comment

What a wicked soundtrack!

In the same sense of not needing to know the chemical makeup of the ink to use a fountain pen, this article offers some important considerations in audio post production that can make the difference in your product sounding The directorprofessional or amateur. One of the most common requests made of sound editors is to “clean up” the dialogue. The process used to accomplish this depends on what issues the soundtrack has to overcome. While the removal of clicks and pops may be relatively easy, the more complex removal of background hum, noise and ambience may be required.

Location Sound

sennheiser-mkh-416On location, TV and film projects utilize a shotgun microphone on a boom for long shots, while many close up shots use a microphone hidden on the subject. Both recording methods bring challenges to audio post production. The difference in sound quality between the close up shots and long shots must be matched as well as the varying backgrounds, unless the sound is recorded in a “controlled environment” like a sound stage. But even if the dialogue to be matched is from two different close up angles (like over the shoulder shots for a conversation), the general ambience differences may still be extreme. Hum, mouth noises and background noise should be removed or reduced.

ADR & Dialogue Replacement

ADR process described by Director Peter Masterson and Actor Gene Hackman during dialogue replacement for “Full Moon Over Blue Water” ~ 1988.  Although the process has not changed the technology is now all digital. Sound Works has been doing ADR since the mid 80’s.


Sometimes the location sound is distorted so badly that the director may be tempted to start over and re-shoot the entire scene from scratch. Given the cost of a production crew, location costs and rentals, this may not be the most cost-effective solution. ADR can be an effective solution for replacing individual lines. It requires the skill of the actors and ADR engineer to match the performance and sync. The engineer has a number of tools to assist with ADR. For example, Sound Works has software that will lock-step the sync of the new performance to the original recording allowing the actor to concentrate on expressing the line properly. In post production, the qualities of the performances can be matched in tonal quality and proximity to the camera. The voice “tone” is adjusted to make the voice more “up-front” for the close up reads.

Background Sounds

Location sound engineers should always record background ambience to allow the audio post people more options when matching dialogue. For example, if ADR is to istock_000001786036mediumbe used, the re-recorded line will have little or no ambience compared to the replaced location line. But the previously-recorded location ambience can be added to the ADR sections resulting in a seamless-sounding dialogue track.

But let’s say the shot is at sundown and the volume level of crickets in the background is changing every 30 seconds. It is possible to sample the undesired crickets and peel them out of the sound track leaving the desired dialogue unaffected. At Sound Works, we have several processes to remove or reduce background noise. This is the same process used in our forensic audio service. Removing undesired background noise could eliminate the need for ADR or reshooting the entire scene. And THAT makes the sound editor’s job one less headache!

February 24, 2009 at 12:08 am Leave a comment

Hold the noise – give me a double serving of that voice

Yesterday, Sound Works had to dig into its forensic audio tool kit to help restore two recordings for two different cases.  Recordings that need enhancement are rarely the same.  Depending on the location, equipment and recording process, each recording pretty much mandates a different restoration solution.

2-way Radio
police-radioThis enhancement challenge was to remove noise and increase intelligibility of a police officer’s two-way radio recording. Although taken from a digital logger, the noise at the scene had to be analyzed. We applied several restoration processes and were able to “scoop” the conversation away from the noise.  The end result was a more intelligible recording.  Our work was then prepared as a trial exhibit by indexing the critical points on a compact disc for easy access. In sum, all the work produced a professional, presentable product for judge and jury.


Phone Recording
suction-micThe second job was a recorded phone conversation for a civil case.  The phone conversation was recorded with a common suction cup telephone pickup attached to a digital recorder. Unfortunately, the pickup barely recorded the distant side of the conversation while the local side of the conversation was fine.

We were able to segment the two voices and process the audio of each side of the conversation differently.  The distant voice required the volume to be raised 80db – the equivalent to the volume of a very noisy office.  And just a couple of db improvement can make a big difference….

Perception of db changes in Sound

Level change (dB)




Barely perceptible

2 × as loud


Clearly perceptible

3 × as loud


Twice as loud

10 × as loud


As you can imagine, increasing the volume to this extent raised the general ambient noise level.  One of our applications has the amazing ability to differentiate the noise from the voice allowing layers of noise to be reduced. Once the distant voice was improved, it was then merged back with the normal voice.  Our work, again, was supplied to the client in a trial-ready presentation form.

Note that each of these projects were recorded with digital devices – THAT fact alone does not insure a good-quality recording. The recorder can only capture only what it “hears”.

If you found this interesting also see “Shhh … I’m listening”, “But it’s a digital recording” and  It seemed impossible to pick out the voice buried amongst the restaurant bedlam on the recording.”

By Dwight Cook




February 19, 2009 at 6:12 pm Leave a comment

What baggage charges?

baggageIn its current ad campaign, Southwest Airlines makes fun of their competitors charging extra fees for checked bags, window seats, aisle seats, snacks, curbside checking in, and fuel surcharges. This smart marketing allows Southwest to differentiate itself from other airlines. (See this article from aviation website Flightglobal.) While their competition is defending the need to pass along “extra” or “ancillary” charges, Southwest Airlines can successfully price its flights without charging for all the extras!

 Production Project Pricing

There are few of us out there who don’t feel we’re being nickel-and-dimed to death by most services these days. And while billing by the hour is palatable for some, even law firms are exhibiting a willingness to change. Most Agency and Corporate work now expects a fixed-cost project price because it “sets” the budget. And with the economy causing budgets to further tighten, I expect the hourly rate to rapidly disappear.  At Sound Works, we have been moving toward a flat-fee project price for years.  We invite our clients to communicate with us when setting up their budget.  Changing billing practices can not only create more teamwork on the job, but generate a win-win partnership for the customer and production company.

by Dwight Cook



February 13, 2009 at 9:00 pm Leave a comment

Shhh … I’m listening

One of the best kept secrets: Sound Works had been doing forensic audio and expert witness services for many years.  We restore noisy recordings and can tell if recorded evidence has been tampered with. The same technology used in audio forensics to enhance intelligible conversation can reduce background noise audio on any recorded event from focus groups to film shoots.


ssshOver the years, we have cleaned up audio from corporate video, film projects, small hand-held recorders as well as re-mastering music. The technology is amazing! We have successfully peeled away background noise, a chirping bird, crickets, tape hiss, vinyl or record surface noise, airplanes, motors and air conditioners to name a few.


One of my favorite success stories was the restoration of a music video. It was a large, multi-camera shoot of a live concert. The power supply in the sound truck audio console went bad and created loud pops across all channels of the recorded audio. When the media arrived at Sound Works, we identified the location of each pop and removed them. But it gets even better… Just editing the pops out of the music would have caused gaps and jumps in the songs. Our engineers were able to interpolate the missing sound and create a seamless removal of the pop. It’s like the problem never existed.


If you have a bad recording … think restoration. All may not be lost – it may save some costs and make you a hero.


If you liked this you may also want to read:


But it’s a digital recording” – have you ever hear those words from one of your clients?

It seemed impossible to pick out the voice buried amongst the restaurant bedlam on the recording

By Dwight Cook

January 29, 2009 at 11:50 pm Leave a comment

But it’s a digital recording

“But it’s a digital recording” – have you ever hear those words from one of your clients?

You got the phone call last week. A young lady is being dismissed from her job because of what appears to be sexual harassment.  Of course, there is the little problem of her words against those of the harassing supervisor. Then you hear the magic words, “I recorded the whole conversation on one of those tiny digital recorders.”  digital-recorder Well, all right then – We have a case and who could dispute the incident when you can hear it as it happened.  So you ask the lady for the recording in order to educate yourself to the specifics of the incident… And that’s where the trouble starts.  Sure, you can hear every word your client says but, unfortunately, not the supervisor who makes the offending statements.  Well, “it’s a Digital recording isn’t it? – Why is it not perfect?”

Here is where a little knowledge can be dangerous.  Yes, digital recording is a way to ensure “perfect” storage of the sound and/or picture that you are recording. However, this has nothing to do with the initial quality of the recording.  The problem is that you can have a wonderfully pristine recording of bad sound.  The device doesn’t know any difference; it will record and save “perfectly” both the good and the bad.  So, what can you do now?

You could see if the incident could be repeated and, perhaps, catch the supervisor in the act yet again and maybe get a better recording.  Or you could have the present tape transcribed and let the transcriber use their best judgment as to what the hard-to-hear sections contain. However, the best choice is to use an expert in “enhancing” low-quality recordings.  Whether you call it Audio Forensics or Audio Enhancement, it all boils down to the same thing – an experienced, sound technician with not only the right tools to create a usable piece of evidence, but the subjective knowledge to give you the best possible product. Today, everybody seems to have some software they got for free off the internet and is more than willing to work for next to nothing.  Beware! – As the old saying goes, “You get what you pay for.”  And you can’t substitute technology for intelligence.  Much of the time, the real problem with the recording IS the microphone is “stupid” (it doesn’t make a decision to tune-out the background noises from the voices you are trying to hear) and it is not a human brain.  Think of being at a cocktail party with a hundred other folks – You are still able to have a conversation with one other person, ignoring all the other sounds around you.  This is the miracle of the human brain’s audio ability.  It takes an experienced and trained engineer to act as the “brain” after the fact and uncover the hidden audio.

You well know that there is nothing better than a good eyewitness and what better a witness than a clean and intelligible recording of what really happened.

by Mark Meyer


January 27, 2009 at 10:58 pm Leave a comment

It seemed impossible to pick out the voice buried amongst the restaurant bedlam on the recording


Forensic Audio Enhancement

by Danny Reeves and Dwight Cook

Sometimes it seems impossible to discern the details on a recording.  There is too much background noise, or the volume is too low. The solution is a process called Forensic Audio Enhancement; the attempt to correct defects in recorded audio.  Defects might include clicks, hum, buzz, pops, excessive background noise and poor signal strength, any of which can lose a case.

But now technology has progressed to such a point that these defects are not altogether impossible to overcome. There are two basic types of enhancement that can clear up your recording; listenability and/or intelligibility of the sound source and both are non-destructive.

Easy on the ears

Listenability enhancement is a relatively simple procedure applying equalization (EQ), compression, amplitude increase or limiters to an audio recording which is already intelligible, but needs to be made more listenable.

Easy on the brain

Intelligibility enhancement is a more complex and demanding engineering task.  Enhancement procedures involve complex scientific filtering, digital compression, digital EQ and amplitude increase and limiting.  Sometimes there is the need to target small sections of the recording with “region specific” processing.

For the forensic audio engineer, this requires knowledge of the physics of sound, human auditory perception, phonetics, critical bands, as well as knowledge of electronics and professional audio recording techniques, and of course experience. An engineer’s past experience is key to knowing what to do and can save you time and money in the discovery process. The results can be impressive, with previously unintelligible dialogue becoming intelligible and coherent. In some cases, previously unknown audio events are uncovered!

What is the typical process for enhancing audio?  There are four basic steps in the forensic audio enhancement process.

  1. TRANSFER the source recording to a digital format.  The source recording can be any of the following: micro-cassette, regular cassette, any tape based recording format; digital hand held recorders, police videos and voicemail.
  2. EVALUATE the material and then develop an enhancement plan.
  3. EXECUTE the enhancement plan until the desired outcome is reached.
  4. CREATE a final digital master of the original recording along with the final enhanced version.

Double Check

Make sure that your audio enhancement studio is able to offer a certified statement or is available to be deposed for certification. Also make sure that their process has previously been accepted in federal, state, and local courts for credibility.

Danny Reeves is an audio engineer, Dwight Cook an owner of Sound Works, Houston who offers forensic audio services including enhancement.


January 13, 2009 at 6:50 pm Leave a comment


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