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Back to Archives | Back to September 2007 Contents 

Compensating for Noise in Law Enforcement Communications

By Robert E. Lee Jr., Supervisory Special Agent (Retired), U.S. Federal Bureau of Investigation; Member of the IACP Communications and Technology Committee

aw enforcement officers routinely find themselves operating in noisy environments. Despite enhancements in the variety of communications tools available to officers, effective communication in tactical operations continues to rely upon voice communications using radios. When confronted with excessive noise, officers and administrators must be aware that radio transmissions may be affected and that various procedures, equipment, and tactics can be used to solve many noise-related problems to ensure safety and effectiveness.

The Challenges of Noise

We’ve all seen it on television and in the movies: a technical specialist takes an audio recording, plays it through an electronic gizmo, isolates a sound, and plays something that had been heretofore hidden from the human ear. It seems that being able to isolate parts of audible messages can be of benefit to law enforcement practitioners, but knowing what to isolate and when is difficult. Sophisticated equipment and technical know-how are helpful but often take too long to be meaningful in tactical circumstances.

Each day law enforcement practitioners find themselves in a wide range of environments, each with their own challenges, including noise. When searching a building in the middle of the night, for example, the operation might be conducted in quiet, with no more noise than the breeze of a ventilation system, or it might be conducted while a burglar alarm is sounding throughout the building. In each case, personnel are dependent on radio communications to assist in coordinating the response and keeping others advised of progress.

Law enforcement communications are generally broken into four categories: dispatch, tactical, strategic, and informational. Although each has its specific purpose and communication mode, they all share the common reality that when radio is used to relay messages, there is usually some noise in the vicinity of the people transmitting and receiving the messages.

A well-designed dispatch center will include noise reduction mechanisms, and dispatch consoles can be located in quiet rooms. In addition, high-quality, comfortable headsets with close-range microphones can minimize noise and its impact. Sometimes noise can result from the radio system itself, so it is important that skilled professionals install and maintain consoles and other equipment to ensure their isolation from nearby sources of interference.

With the advent of shared systems and consolidated dispatch centers, technical and dispatch issues may not be under the direct control of law enforcement administrators; therefore, police leaders should exert their influence through governance and processes at their disposal to keep field personnel safe.

The real focus for police leaders is to ensure that field personnel maximize the effectiveness of their communications equipment to keep staff safe and well informed. By controlling purchase decisions, policy, and oversight, police administrators can choose equipment that will work best in the environments they face.

Gordon Graham, a frequent lecturer in risk management for law enforcement, has stated repeatedly, “If it’s predictable, it’s preventable.” And so it is that police leaders must address the effective use of communications equipment in ways that minimize risk.

Communications Overview

All human communication consists essentially of a message sent, transmitted, received, and understood. In the world of electronic communications, this happens with the aid of electronic equipment that takes a message, converts it to electronic signals, transmits it through a medium, and decodes it at the receiving end.

In our daily lives, we see this happen with ease. With e-mail, words are written, encoded, transmitted, and decoded by electronic communications hardware and software. With television, the process is similar, but the output of the transmission is in the form of audio and video. Audio and video can be transmitted through other media as well, and it is no longer uncommon to use Internet Protocol (IP) for this purpose. The importance here is that standards are set in the communications industry to permit equipment to work together effectively. Effectiveness is dependent on the inventions designed for a given purpose and their ability to work well with other equipment used in the process.

A recommended standard for public safety communications is Project 25 (P25). The P25 standard is actually made up of a group of standards designed by practitioners, developers, and manufacturers to allow digital equipment to work together well, primarily in voice communications. The name P25 originally came from an organizing force in public safety communications, the Association of Public-Safety Communications Officials–International (APCO). APCO has defined projects dedicated to the education of its members, the safeguarding of citizens, and improved communications during emergencies. Projects are numbered sequentially, and Project 25 addressed the issue of creating standards for digital communications. Interoperability was less of a problem for analog equipment, which was used before the advent of digital communications.

Law enforcement and the public safety community came to face the industry change from analog to digital communications equipment as older systems were being replaced. Analog equipment became outdated, and manufacturers no longer made new equipment or replacement parts to support old systems. Despite the importance of properly equipping public safety services, the public safety community is responsible for only a very small portion of equipment sales since cellular technology has come to be used by the masses; thus, public safety has less clout in developing standards than might be expected.

Although the P25 standard is important in enabling public safety communications equipment to work together well, it demonstrates that standards have such an important impact on the industry they serve that they take years to develop. However, public safety practitioners, including law enforcement personnel, must know that standards alone do not solve all problems. The importance of selecting appropriate equipment, training users, and developing procedures to effectively use equipment cannot be underrated.

The ability of things to work together is the essence of interoperability. The elements of interoperability play a role in effective communication in a noisy environment, since each message may be diminished by noise in the vicinity of the sender or the receiver and along the transmission route. Interoperability is not the primary focus of this article but must always be recognized as important to communications, since messages that go unheard because equipment is not interoperable can lead to situations just as dangerous as messages unheard because of noise.

Radio is still the essential transmission tool for tactical law enforcement operations.


Noise is sound that is not welcome. In law enforcement, this can be defined as sound that disrupts messages or makes no sense to the circumstances at hand when heard. Sound is the perception of hearing. A voice message is sound sent with the intention of someone hearing it. What is originally perceived as noise may in fact contain a message, with proper interpretation. But without the ability to interpret noise in real time, it cannot be useful for tactical operations.

Some describe noise as being unpleasant or painful. This is very true for an officer finding his way through a building with an alarm sounding or for officers engaged in a foot pursuit that makes its way onto an airport tarmac or into an industrial manufacturing facility. But not all unpleasant sound is noise. In fact, domestic disputes or advice from superiors may contain unpleasant and painful messages, but they come through loud and clear and may be useful in understanding and solving a problem. Sometimes the sound of certain voices is unpleasant as well.

There are other types of messages, such as the written word, or visual cues, that do not involve sound, but as they are not relevant to radio communications, we will not consider them in this discussion. Because law enforcement officers are interested primarily in hearing the human voice when using the radio, this discussion will limit itself to the noise that interferes with the ability to communicate effectively using radios as the tool for transmission.

Normal Noise

To understand the concept of noise, it is necessary to examine the various forms and causes of noise. Upon recognizing these forms and causes, corrective action can be taken.

Ambient noise is the type of noise normally found in a particular environment. To understand noise levels, scientists have conducted surveys to identify ambient noise. For most occupations, ambient noise in the workplace can be measured and corrective action taken to minimize its impact on people who work there regularly. Closing a door can be effective in the workplace to minimize noise, and many offices provide telephone headsets that minimize noise so that telephone conversations can take place without disruption or distraction. In industrial settings, employees may wear earplugs to minimize the impact of noise. Other settings have quiet rooms, in which conversation can take place without the blare of machinery and production equipment. Many of these corrective tools may not be available in everyday law enforcement settings, so additional adaptive strategies may be required.

Ambient noise in the context of law enforcement is not a constant due to the nature of law enforcement activities. Even though law enforcement officers are typically expected to bring an element of control to situations that are out of control, the control they do establish has a variable effect on their environment in regard to noise levels. In more predictable environments, noise can usually be mitigated more effectively.

Places in which law enforcement officers may frequently find themselves include highways, industrial environments, transportation facilities, and entertainment and recreational venues. Sounds related to such places include engine noises, machines, loudspeakers, and human voices. All of these sounds reverberate in their own unique way due to building construction and other peculiarities of amplification or distortion.

Some noise common to the law enforcement work environment may affect radio communications: sirens, engine noise from diesel engine–powered equipment, explosives and gunshots, helicopters, and barking dogs are common background noises in the profession. Officers can grow used to such noise when it is frequently present, and they may forget that they are easily heard over the radio when attempting to communicate with others.

Officers can become desensitized to the common noise around them, whatever their usual assignment. An officer regularly working in a train station eventually stops hearing the train schedules announced over the loudspeaker, but such announcements come through as noise whenever the officer transmits a message via radio. The noise of a crowd at a ball game quickly becomes ambient to the officer working at the ballpark, but it is a great distraction to the recipients of the radio messages the officer transmits.

Some newer sounds have been introduced into law enforcement duties with the growth of some responsibilities. Hazmat and bioterrorism teams bring with them equipment and operating environments that are newer to policing. Colleagues in the fire service have long been aware of the impact of alarms associated with man-down devices or tank-near-empty alarms from self-contained breathing apparatus (SCBA), but they may be new to some police departments who now train in and respond to these emergencies.

It is vital to examine the impact of volume, intensity, and pitch on communications and to seek to minimize this effect. These issues also contribute to whether or not a particular sound comes through as noise at all. Whether the noise in the law enforcement environment is natural or man made, human or mechanical, officers who are aware of noise can take steps to mitigate its effect on their operations. Officers should not allow traffic, alarms, machinery, large crowds, music, or the grunts and groans of workers to keep them from communicating effectively and helping to keep people safe.

Communications under Stress

Even though police officers seem to accustom themselves to working in stressful environments, communications under stress may still reflect the feelings of the moment. In fact, failures in communications are seen to lead to additional stress. This stress is often heard in the volume, intensity, and speed of voice communications transmitted at the time.

Brief messages such as “Officer down!” can come through with the urgency required to gain attention, but without additional information about the location of the down officer, the message may be close to useless. Furthermore, supporting units in such situations benefit substantially from a description of the threat responsible for the down officer, the specific needs of the officers engaging the threat, and directions to the scene.

Dispatch personnel, through their training, experience, and surroundings, can often provide the calm needed to break through the stress-filled messages transmitted by officers in the field. Much of their talent has been acquired by handling similar communications via telephone from citizens requesting help by dialing 9-1-1. Using their polished vocal demeanor, dispatch personnel can assemble information in a meaningful way by effectively guiding communications and probing for all required information. Administrators should check to see if the increasing use of mobile data terminals for dispatch information has diminished the ability of dispatch personnel to make a rapid transition to an emergency event that includes tactical radio communications.

In stressful situations, one sense that shuts down is hearing. People under stress often fail to hear what is going on around them. A consequence of tactical communication may be that an officer transmitting in a noisy environment may not even realize that it is noisy. The failed communication due to noise then contributes to additional stress as the officer realizes that the message was not heard or understood. Consequently, a situation that requires controlled behavior and a controlled response may deteriorate further.

Even if hearing does remain functional, voice communications under stress are often the worst. People shout, others still fail to hear, and all are distracted by threatening circumstances or other issues needing resolution; as a result, messages often provide unclear information about what is needed and where.

Police should spend time training to deal with the problem of communications under stress. Without forethought and practiced response to these situations, outcomes are likely to be less than satisfactory.

Communications Technology

Communications between humans located within feet of each other are considered to be instantaneous. Electronic communications systems have delays in them that are tolerable but different from direct human-to-human communications. These delays are called latency and vary in length based on the complexity of the system involved. This phenomenon can be noticed when one person transmits a message to another, and someone on the same radio system is nearby. The original speaker can hear his or her own voice speaking some microseconds after the original words have been uttered.

When communications were transmitted in analog form—that is, not in digital form—delay was minimized. But analog transmissions are not efficient in using the radio waves allocated to public safety communications and disallow some methods by which messages can be transmitted, including IP. So digital transmissions are the preferred method and are in fact most like the messages that now get passed over the Internet.

But the human voice does not sound in digits, nor does the human ear hear in digits; both function in analog. For digital transmission to take place, the spoken word (and other sounds) must be changed from analog to digital in order to be transmitted and then converted back when the signal reaches the receiver. This action takes place with the use of a vocoder.

Vocoders are part of every digital radio. A vocoder is a combination of hardware and software that converts analog voice to digital. A vocoder receives a combination of voice and noise and from that input models the information and produces a digital output. When the background noise is louder than the speaker’s voice, there is the chance that the voice will be overridden and will come through as unintelligible.

Variations in how vocoders process information are subject to some government regulation as well as standards development to ensure that a change to improve one area of performance does not adversely affect other areas. This is a common concern in all areas of technological development; vocoders are just one representative.

P25 identifies the Digital Voice Systems, Inc. (DVSI) vocoder as its standard. It was selected because of its ability to deliver high-quality speech at low bit rates in harsh environments.

Despite the best efforts to provide high-quality transmission tools for public safety, however, noise continues to be a problem for the law enforcement profession.

Adapting to Noise through Training, Discipline, and Equipment

Like the adage used for traffic safety, education, engineering, and enforcement are the areas of focus for combating the problem of noise in public safety communications.

Establishing discipline in communications begins in basic recruit training. Tactics and operations training must include training specifically targeting communications. Practical exercises in such training should stress the importance of clear messages and how to speak on the radio. It should also include discussion about the types of environments in which law enforcement officers may find themselves, the noise existing in these environments, and methods to mitigate such noise.

Agencies that train personnel in house should always include training on the specific equipment that will be used in the field. To use digital radio and trunked radio systems, which have their own intricacies, effectively, detailed knowledge of these systems is required. In crisis situations, personnel revert to the training they remember or what was last on their mind.

Time should be devoted to talking about the impact of noise on all communications, in face-to-face communication as well as on the radio. Trainees should have the opportunity to hear good and bad transmissions and to discuss what can be done to improve circumstances in problematic situations.

For personnel already deployed, agencies should create mechanisms for continued training at roll call or inservice lessons. Supervisory staff should bear the responsibility of administering such training and should be given the tools to help educate their subordinates. It may be useful to introduce reminders in the form of stickers placed in police cars, radio reminders from dispatch, or even pens or computer wallpaper to remind people of the following piece of wisdom: “If you can’t be heard, you can’t be helped!”

Supervisors should also take care to correct poor performance when it comes to radio discipline. The responsibility extends up the chain: field personnel should also be required to demonstrate that they understand the principles of communications effectiveness and equipment operation. If necessary, a general order on the topic can be issued to allow field personnel, supervisors, and dispatch personnel to understand the intentions of the executive and the consequences for misuse or poor performance.

One advantage to digital radio is the automatic identification of each transmitting unit. If a particular unit is too often off the mark, then counseling can be provided directly to the user of a particular piece of equipment. Agencies routinely record radio communications, which can be used as a tool to demonstrate good and bad performance from real-world situations with local consequences.

Other instructions to field personnel might include the following. When feasible, dispatch personnel should be allowed to operate in a more noise-controlled environment to relay messages to avoid confusion. Wherever possible, noise sources such as machines or engines that are not required should be turned off. Personnel should be instructed to keep their distance from noise sources so that their transmissions can be better heard. When field personnel respond, they should close their car windows so that sirens, traffic, and wind noise do not interfere with communications. If headsets are available for personnel and the environment is safe, then they should be used. Noise-cancelling microphones can be used in environments of excessive noise, but vocoders should be checked to ensure that they can still pick up the user’s voice, and the microphones should always be used in accordance with manufacturers’ guidelines.


This article has shown how important the human voice is in the continuing work of law enforcement. The reality of communications under stress in hostile environments with unusual equipment and high expectations is far removed from a simple home telephone conversation. The stress of unusual circumstances on humans should be considered in the design, purchase, and application of equipment used in the profession. There is no one-size-fits-all solution to the challenge of communicating effectively in varying environments.

Law enforcement leaders should review their communications needs and determine the range of environments that officers may confront. Equipment should be tested to allow personnel to hear what happens in various environments. Personnel should exercise caution if they use machines or loud tools in places that will strain the performance of equipment and other personnel. Radio is a law enforcement lifeline—don’t let noise weaken it.■



From The Police Chief, vol. 74, no. 9, September 2007. Copyright held by the International Association of Chiefs of Police, 515 North Washington Street, Alexandria, VA 22314 USA.

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