My growing collection of unusual noises...

I created this page to help my friends with scanners & ham radios identify the growing number of new & unusual sounds they might hear when monitoring outside the amateur bands.

I'm always looking for new additions to this page - if you have high-quality audio recordings that you want added to the database here, contact me.

All sounds are in MP3 format. Click on the title of each to play them.

Section 1 - Unit Identifiers

Motorola MDC-1200 - This is the most common form of unit ID found in public safety. This is either broadcast at the start or the end of a unit's transmission (or both, if you so choose to have it programmed that way). The user's radio can also be programmed to emit a tone on key-up (to remind the user to wait before speaking, as the unit's mic is not activated until the ID is sent).

MDC-1200 Preamble - This added feature of the MDC signaling system is designed to allow a properly programmed radio to mute the ID signal part of the transmission. The raw burst of data tells the radio to mute the speaker audio for a pre-determined length of time (usually 400 or 500 ms). If the radio is programmed correctly, the end-user (or dispatcher) would not hear this sound at all, only the person's voice.

MDC-1200 Echo - This sound is most commonly heard in a police cruiser or ambulance cab. What you are hearing is the very end of the 'wait tone' echoing off the inside of the vehicle and being picked up by the mic. Also, there are several Motorola radios that emit an "ok" beep, just like a key press, when the PTT is used. Certain models of the Maxtrac's and 'Pro' series radios were famous for this. (Updated - Thanks Paxton!)

MODAT - This is an older form of unit ID by Motorola. This is actually a slower-speed data transmission rate than MDC-1200, and what makes it truly unique is that the actual sound of the ID varies when you change the ID code. Baltimore FD and LAPD used to use this form of ID before they both went to digital trunking. MONOC EMS in Monmouth & Ocean Counties (NJ) use this currently.

GE STAR - This form of unit ID was General Electric's answer to MDC-1200 when they where still involved in the 2-way business (before selling that division to Ericsson).

GE G-Star 400 - I recorded this while monitoring Voorhees PD in Camden County, NJ. Only about half of the patrol units on a shift had this at the end of their transmissions. (thanks to Kevin from RR for the info!)

Section 2 - Voice Scrambling & Encryption

Motorola DVP XL - This recording is from the Gloucester Twp. PD in Camden County, NJ. The dispatcher usually transmits a short warning tone & then calls the units she needs to speak to in 'secure' mode. As you can hear, the units in the field respond back to dispatch 'in the clear'. Gloucester Twp uses this only as needed, and I've never heard any department use this full-time.

AES & DES Encryption - This is the most wide-spread use of encryption on public-safety radio systems at this time.. This is almost never used on analog systems, because it has a detrimental effect on the quality of the decoded audio. Most first-generation Uniden digital scanners do not block the audio playback of encrypted signals, and I was able to get a very clean copy from my BC-796D before I sold it. This recording is from the Franklin Twp. trunk system here in NJ. If you were to stumble across this with an analog receiver, it would sound identical to the ASTRO sample in the next section. The primary difference between AES & DES is the cipher strength: DES is 64-bit and AES is 256-bit. (NOTE - if anyone has the ability to get a recoding of encryption on a M/A-Com ProVoice system, I'd greatly appreciate it!)

Marconi DM8000 DES - Visitor submission

MASC Voice Scrambling - Visitor submission

Transcrypt International 410 Voice Scrambling - Visitor submission

Transcrypt International 430 Voice Scrambling - Visitor submission

Transcrypt International 460 Voice Scrambling - Visitor submission

FFT-Style Voice Scrambling - Visitor submission

Midian TVS-2 Voice Scrambling (standard single-hop) - Visitor submission

Midian TVS-2 Voice Scrambling (high security double-hop) - Visitor submission

Selectone ST-25 Rolling Code Sweeping Scrambler - Visitor submission

Split-Band Voice Scrambling - Visitor submission

MX COM Variable Split Band (VSB) Scrambling - Visitor submission

Static Voice Inversion - Visitor submission

Unknown Voice Scrambling (possibly military) - Visitor submission

Rolling Code Speech Frequency Inversion - Thanks Warren!

Section 3 - Digital Voice Formats

Motorola ASTRO VSELP - This was Motorola's first digital voice solution marketed under the ASTRO name. This was a in-house modification to the Vector Sum Excited Linear Predictive standard that was used in the first TDMA cell phones. Motorola also modified this into the IDEN format that is used by NEXTEL phones (see below). Very few jurisdictions use this type of system anymore (Trenton, NJ & Cleveland, OH). This is not a Project 25-compliant system, and cannot be picked up on any known scanner (probably why the cities that use it are keeping it!). (updated sample)

Motorola ASTRO IMBE - This is Motorola's current ASTRO voice format offering. This type of emission is known as C4FM, and the technology in use is the IMBE (Improved Multi-Band Excitation) vocoder from Digital Voice Systems Inc. This is an much better sample of decoded audio from the Bucks County, PA 500 MHz trunk system (compared to the old sample here from Philadelphia's system) . (updated sample)

M/A-Com ProVoice - This is the current form of digital voice originally developed by Ericsson. This is also an IMBE signal style, but is not Project 25 compliant (whereas Motorola's is). The decoded voice clip is courtesy of a fellow RadioReference.com member involved with the deployment of Oklahoma City's new EDACS trunk system: OKC Police. There is currently no scanner or receiver that can decode this (the format is proprietary, and M/A-Com will not share the specifics).

M/A-Com Aegis - This was the first-generation digital voice solution from General Electric. This format is not well liked because the decoded voice leaves much to be desired. It is not Project 25 compliant, nor can it inter-mix with ProVoice. As with ProVoice, there is no scanner or receiver that can decode this.

ICOM D-STAR - This is the new digital audio format in use by the D-STAR amateur radio system. This is what you would hear if you came across a D-STAR repeater with a regular analog amateur radio. This is an AMBE vocoder that uses the GMSK modulation style (similar to the world-wide GSM cell phone standard).

ICOM D-STAR vs. FM - This is KC5ZRQ testing the outer range limits of D-STAR vs. analog FM on simplex. This is a pretty impressive example of how D-STAR will hold it's 'intelligibility', while the FM capture degraded to a pretty bad level.

Section 4 - Trunked Radio Systems

First-Generation Motorola Control Channel - The title is pretty self-explanatory - This was the 3600 baud data stream used in the first Type-I trunk systems.

Current Motorola Control Channel (SmartNet) - This is the current control channel style in use for most modern Motorola Type-I, Type-II, and Type-IIi Hybrid systems. This is a 3600 baud data stream, and was sampled from the East Brunswick, NJ SmartNet system.

Current Motorola Control Channel (SmartZone) - This control channel stream is very similar to the SmartNet stream above, but was recorded from the NJ State Police Troop B SmartZone system. I'm unsure if the difference in the sound is because the system is a SmartZone, or because of the much larger volume of data being transmitted.

Motorola SmartZone OmniLink Control Channel - In the last few months of 2006, the NJSP completed an upgrade to the statewide trunked radio system. They upgraded the 3 separate SmartZone system in to one seamless OmniLink setup. Users from any part of the state can now leave their radios turned to their primary home talkgroup, and the system will follow them, even if they cross system boundaries. The upgrade seems to have added some interesting characteristics to the sound of the data stream.

APCO Project-25 Control Channel - This is the new 'top-of-the-line' when it comes to digital trunk systems. Project-25 trunking is a completely digital, vendor-independent  specification that was initially developed by Motorola, and now has product offerings & support from Kenwood, EF Johnson, & Relm/BK Radio. The system specification allows no analog voice, and is deployed as C4FM or CQPSK-LSM (Compatible Quadrature Phase Shift Keying - Linear Simulcast Modulation) if sent at a 12.5 KHz spread. If the system is set at the new 6.25 KHz spacing, it is just known as CQPSK. This is a 9600 baud data stream.

M/A-Com EDACS Wideband Control Channel - This is the most common form of control channel used in EDACS systems. This is a 9600 baud data stream. When the system is passing voice traffic, you can actually hear the rhythm of the data change.

M/A-Com EDACS Narrowband Control Channel - This is a very seldom seen variant of the standard EDACS system. Here in NJ, Verona Twp. on UHF and Trump Plaza Casino on 900 MHz use this system. This is a 4800 baud data stream.

M/A-Com OpenSky - This is the latest technology system to come out of M/A-Com. This system is basically a wide-area 'computer network'. Every radio has an IP address, and the mobiles can fully support voice & data simultaneously (i.e. - an officer's MDT). This system utilizes the AMBE vocoder (similar to the ICOM D-STAR system), and transmits over a 4:1 TDMA broadcast format. The fundamental design of this system is completely different compared to a Motorola or EDACS system - They use their control channel to tell units on the system to switch to different voice frequencies for reception of radio traffic. OpenSky sends the voice component back over the same stream that carries the control data. This sample came from the Pennsylvania state-wide system. There is currently no form of receiver that can decode this system.

TETRA - This is Motorola's hottest selling trunking protocol everywhere else in the world outside the United States. The system is built around a 100% full-time encryption standard.

MPT-1327 - This is a trunking protocol that is very popular in the UK. There are very few systems here in US that use this (Decatur, TX and Douglas County, WA). It's quite an interesting fact to note that the Metropolitan Police in London use a Motorola Type-II system instead of one of these. There is currently no form of receiver that can decode this system.

Motorola iDEN - I figured I'd add this here because the iDEN networks used by NEXTEL, Telus, SouthernLinc, etc. are a derivative of Motorola's older VSELP digital trunking transmitted over a standard 6:1 TDMA cell format. This is what it sounds like in the raw.

Motorola SpectraTac Receiver - The NJSP system used to use this model of receiver with a 'voting' comparator to mange incoming signals from the multiple receive sites connected to the controller. Since the remote links are never turned off, and always transmitting, they send a 2175 Hz. tone when not broadcasting audio. What you are hearing here is the split-second delay between the Trooper ending his transmission, and the comparator realizing that it needs to switch off broadcasting that receiver. (Thanks Steve!)