At Somerdata, we have selected for you the pick of the best around, and where we don’t carry them ourselves, we will recommend the best solution for you.

Unlike Video recording, audio can be quite difficult to understand and there are still a plethora of formats, rates, technologies and so on to choose from.

So, first try and define what you want to achieve, then compromise to what you can get ( and afford!).

Here are some questions to pose, only you can supply the answers.

1. Is my target benign or hostile? How will they react to discovery of their being recorded? Do I need to tell them beforehand? ( you might need to do some research on lawful intercept and fair usage in the territory in which you operate.)

2. Is my target stationary or mobile? Do they visit one location or many?

3. How close can I get?

4. Can I get to the target site(s) safely before  and /or after the surveillance period?

5. How long is the surveillance period? Is surveillance unattended? Does it need immediate reaction to events?

6. Do my recordings need to be presented as reviewable evidence, especially in a court of law.?

7. Does my device need to be self-powered? How physically robust does it need to be? Are there size and packaging constraints?

8. Does the device need to be protected from counter-measures and interception? what happens if recordings fall into the wrong hands or transmissions are intercepted by a third party?

9. How much is my data worth? How much am I prepared to spend to collect it?

If you’ve answered ALL of those questions then you probably already know enough to make your own selection and you don’t need any more advice. Carry on!

For everyone else,  let’s look at the options, technologies and practical solutions.

Firstly, if you carry a mobile phone, then you already have a mobile audio recorder. Put it on the desk, point it at your target and press record. The quality will be ok and you’ll get something. Now here’s the weird thing. When you come to play it back, you’ll suddenly notice all sorts of strange noises you didn’t hear when you made the recording. Rustling paper, room echo, road noise, and a hundred other liltte noises, some quite distracting. With luck you may even have recorded something useful. Why is this?

Well, the human auditory system is a remarkable instrument. It can filter out extraneous noise, correlate muti-path echoes, focus on point sources and acts as a very sophisticated filtering system especially when coupled with eyesight. Human ears have a very wide dynamic range (>120dB) meaning we can hear whispers and jet engines with equal clarity, but we also non-linearly favour speech frequencies – we hear in the range 300 to 6 kHz more distinctly than in frequencies outside this range. And this also varies with age.

Crucially though, we hear in Stereo using two ears. This not only gives us twice the sensitivity but we are able to give spatial resolution to what we hear – where it is, how fast it’s moving, separation of multiple sources into distinct focal points.

So technically, the mobile phone is going to struggle a bit to compete. It’s  probably mono, limited dynamic range, limited frequency range and doesn’t match the human ear response.

Which leads us to the grown-ups – dedicated recorders and transmission systems designed specifically to work in this environment.

First Recorders.

Dedicated audio recorders for use in covert and /or surveillance operations generally  need to be physically small, robust, high quality and easy to operate. In addition, they may need to have long recording time, be secure if mislaid, and invisible to counter-measures.  Some if not all of these are contradictory and require practical compromises.

Lets look at some of these.

Quality – by which we mean intelligibility and repeatability.

We need to be able to understand the recording and probably listen to it many times without degradation. Repeatability comes from digitising the audio, then using a high-quality medium to store the resultant digits. Nowadays this means solid-state (semiconductor) . Not infallible, but better than mechanical systems like tape, disk or cd/dvd which are easliy damaged.

Intelligibilty comes about through a combination of dynamic range ( the ratio of the loudest sound to the quietest) and frequency range ( bass to treble).

Digitisation involves cutting your nice analogue signal into thousands of bits that take up a lot more space and take longer to transmit than the original, so the concept of compression was introduced to compenaste.  This is not the place to debate compression algorthms, suffice it to say that compression, especially non-reversible, is generally bad for intelligibility. Digitisation also creates its own limits. As a rule of thumb,  you need to digitise at twice the highest frequency you want to record at – as a practical  example, 8kHz of voice bandwidth needs to be digitised at 16KHz. ( For comparison, audio CD quality  digitises at about 44kHz to get a HiFi acceptable bandwidth of 20kHz).  Note though that the number of bits created also doubles, so does the storage capacity and the transmission rate.  In general you need the highest sampling rate you can afford ( although there is no point in outsripping the capability of you microphone). And from an intelligence gathering point of view, you may want to include a wider bandwidth than is strictly necessary for voice, to improve spatial information or pick up extraneous sound information that gives context to the operation.

The other determinant of quality is the number of bits per sample, the quantization level. 8, 10, 12,14 and 16 bits are common. The practical effect of quantization is to largely determine the noise floor, or put another way, the overall signal-to-noise ratio and thus the dynamic range. The more bits per sample  used, the lower the noise floor and the wider the dynamic range; so 10 is good, 16 is better. Translated to analogue quantities, 10 bits is about 60dB ,  16 bits can represent about 96dB of Signal to Noise ratio. Of course this is not the only determinant of system noise -  power supplies, microphone and pre-amplifier semiconductor noise may combine to dominate. And as usual there is a price to pay for more bits, in power consumption, download/transmission time  and storage space required

Discrete – or in other words very small and unobtrusive, preferably invisible. Packing a lot of data into a very small space is a challenge for both microelectronics and power supplies. In fact, portable device size is  almost always determined by the battery size which in turn is determined by the power consumption and operating time of the electronics -which in turn is determined by sampling rate and storage technology…… etc.!

Invisible is still a bit tricky but consider hiding in plain view – a pen, a key fob, a usb stick or a bluetooth earpiece are all available and ignored by most people.

Secure – faced with the inevitability of losing your recorder at some point, what about its content? Would you want that falling into the wrong hands ? (ie not yours).  Securing the contents of the recorder is vital, so consider using a record-only device. This may sound strange bt what it really means is beign able to retireve the data only under controlled conditons. A password protected recorder/replayer is a good start but most passwords can be cracked quite readily because they are created by people who liketo be able to remember them so tend to submit to computerised brute force attack quite readily.

Encrypting the stored data is another help, now you need a password ( you did set one didn’t you….!)  and a key. But encryption also takes up storage space, consumes power and is not readily available on simple devices.  Storing the data in an unfamiliar format, proprietary or obscure is another method. users now need access to a format converter which may be unpublished or simply unavailable. This is almost as effective as encryption and effectively limits access at no overhead cost to the device.

Alternatives to Recorders

The obvious alternative to recorders is direct transmission and the uninitiated often say, “all i need is a microphone with a transmitter and i can use wireless – i don’t need a recorder near my target”. Let’s examine that in the same technical way as we did above.

Wireless transmitters suffer many of the same constraints as recorders with a few added. Firstly, a microphone or audio gathering system still needs to be in the right place. It needs a power supply, a transmitter and an antenna. If it needs to be externally controlled it needs a receiver as well.  Wireless transmissions are subject to strict regulation – you can’t just use any part of the wireless spectrum for your transceiver. In fact there are very few parts of the spectrum available to non-broadcast or military devices and they come in distinct bands, for ecample 900MHz, 1.8GHz, 2.5Ghz, 433MHz, 27Mhz and so on. Why is this important? Firstly, these bands are already heavily used -cellular phone networks, bluetooth, zigbee, low power radio, radio controlled models and so on. Secondly and more importantly, their transmissibility varies with frequency or wavelength if you prefer. Short wavelengths ( higher frequencies) travel in straighter paths, the so-called line of sight problem. Short wavelenght radio  doesn’t travel round corners. So shaped antennae are required that ‘point’ signals in the desired direction. Perversely, for this argment, the more useful longer wavelengths that can travel further and  bend a bit, need physically larger antennae. In the case of the longer wavelengths, a quarter wave antenna can be half a metre long. Go lower in frequency and we start to talk several metres (or several equivalent metres) with folded arrays and reflectors etc. These can hardly be described as discrete.

So surveillance trnasmitters of this type tend to concentrate on the shorter wavelengths. For example Bluetooth operates in the 2.5GHz region. Consequently the range is limited and if someone happens to park a bus or a truck in front your transmitter, or it rains heavily, or there are a lot of other bluetooth devices around then the range may be zero as far as you are concerned!.

The effects of this can be overcome a little by boosting the power of the transmitter, bt leaving aside the increased power supply or batter needed to do this, this leads to the next problem -detection and counter-measures.

Clearly, a wireless transmitter by design is capable of being found by a receiver. If it can be found by your receiver then it can be found by someone else’s. Or more likely by a sweeping spectrum analyser designed to find it.  Strategies to overcome this include spread-spectrum, chirp or burst transmission and sweep detector detection. These add to the complexity, cost and detract from the reliability.

So what about a hybrid? Why not record the data, then download it wirelessly so you don’t have to retrieve it.?

In two words -see above. The problem does not go away or get better. The wireless link now has to be remotely activated, so a transmitter and receiver is required. And an antenna. And a power supply. And a recorder. And let’s think about the data transmission characteristics.

Suppose a recorder has been running for a couple of days at a good quality. It may have accumulated 3-400MBytes of data. This now has to be downloaded. Assume the link is capable of good quality bluetooth  rates, say 100kbps to make the sums easy. The time to download this data assuming uninterrupted and error-free, is 400*8*1000 kb (kilobits) /100 (kilobits per sec) = 32000 seconds or about 9 hours!

Now clearly we can hope for better than this – low power data rates are gradually climbing but even at 1Mbps this is still approximately 1 hour. Higher data rates approaching WiFi rates are available but only at significant power cost. And of course the transmitter can still be detected, and any simple electromagnetic shielding around the target will nullify the transmistter. (Chicken wire works well).

The conclusion to this is that there is no simple answer. Each situation may require a different solution and you need a toolbox of them to deliver results.

Hopefully at Somerdata we can provide you with some of these tools, advice and even the names of Companies  who provide the solutions we don’t. !

Model SSAS-A37 A37 Data sheet comes in 2 or 8GByte capacity and features a small size with a high capacity internal rechargeable battery for up to 40 hours continuous high quality recording.

SSAS-A37

Model SSAS-A9 Plus SSAS-A9 Data sheet has even longer single charge recording time, up to 210 hours and also has an integrated fast USB 2.0 interface for speedy downloads and local replay for review monitoring.

SSAS-A9

Model SSAS-U49 SSAS-U49 Data sheet is a unique directional recorder that includes multi-microphone noise cancelling technology for unbeatable performance including a recording  range up to 15 m from the target!.  Noise cancelling also contributes to the very wide dynamic range of this recorder, up to 80 dBm.

SSAS-U49

PC-VDR - E1/PRI Disk Recorder/Replayer

PC-VDR is a versatile range of portable, transportable and rack-mount Disk Recorders for real-time digital data recording and replay of E1/PRI digital communications signals.

Captured signals can be analysed for content, bit-by-bit dubbed for secure archiving and audit control, replayed in real-time, audio timeslots extracted to WAV files, SS7 signalling timeslots hdlc decoded and saved as pcap files for decoding by Wireshark.

Typical applications include surveillance, archiving, monitoring & logging for interception, testing and fault capture. By providing real-time recording and replay capabilities PC-VDR can be used to complement existing equipment in digital communications test and analysis applications.

Raster display of timeslot activity

Using Wireshark to display ISUP information

Features

• 2048kbits/s raw data input and output
• BNC and RJ-45 versions
• Selectable 75 Ohms, 120 Ohms or high-impedance inputs
• Recording, Replay and Endless-loop logger software options
• Timeslot Extractor software option

PC-VDR Data Sheet (pdf)

In this case, you want to switch one incoming E1 pair to a one of up to three destinations. perhaps when one of the destination routes is unavailable or goes down.

The diagram shows the routing.

This is easily set up using the supplied Windows app, and will be retained in non-volatile memory until changed again.

Now the opposite, a E1 Selector, selecting one destination from up to 3 sources. This could be the ‘other end’ of your redundant system, or simply a way of selecting a stream for monitoring or routing elsewhere.

Of course, if you have two source and two destination streams you have a simple 2×2 cross-point switch!

Grooming

If you need to select timeslots and coalesce them into a single E1 stream, this is the way to do  it.

You can connect directly to RJ-48 E1 streams or as we’ve shown here, use Baluns from 75Ohm co-axial lines.  High impedance input mode means that your system can connect directly to Protected Monitoring P:oints. You’ll need a framing timeslot in the groomed output, that should be routed from Timeslot 0 of E1 Stream 1. After that, you can choose any of the input stream timeslots to populate the groomed output, including up and down traffic.
And if you need to keep a record of the data, you can use our recording application   to store data streams to disk on your pc.

Monitoring and Recording

For discrete, anonymous or non-invasive monitoring of E1 lines you need to tap into them. In this application we’ve shown how you can make use of our Active Data Taps, E1DT. These can be inserted directly in the main lines to be monitored because they have a direct continuous path so even if the power is out or the devices suffer permanent electrical damage, line continuity is maintained.  High impedance buffers are used via isolating transformers to recover low level signals and split them into two.

This means that two standard inputs of E1UC can be used, one for Tx signals and one for Rx signals. And because E1UC is a 4-port device, two sets of lines can be monitored simultaneously.

The collected signals can be recorded direct to pc, or groomed and sent to another location.

Recording uses a plain format that includes a high-resolution  timecode, data integrity and data management information.  This means that recordings can be archived and retrieved later to be viewed and analysed either as direct files or re-constituted  and replayed as original E1 data streams.  The latter of these is very useful if you want to stress a particular transmission component with the same data repeatedly or to unmask occasional non-repetitive faults during transmission testing.

Multiplexing

For testing, data origination or source data creation, you can use E1UC as a source of E1 data. For repetitive testing, you can create file data with a variety of formats, signalling etc containing data that represents your situation or application. Your source data can also be streamed from another application and multiplexed into a new stream.

E1UC has an internal clock to generate the correct stream rate, or it can accept a system clock from an existing  E1 stream That’s what is shown in this diagram.

If you need any advice on these applications, contact us and we will be pleased to advise. Or if you have applications you would like to share we would be pleased to post them here. And if you think E1UC should be able to do even more then let us know!.

• E1 single – E1DT
• E1  multi-stream E1SS

•   Optical - STM-1/4  Splitter

PC Cards

• STM1/STM 4 – PCI Express  - R2D4
• E1 – PCI - R2D3
• RS422/LVDS Serial- PCI  R2D3

Converters

• E1 to Gigabit Ethernet – CARP Data Server
• Gigabit Ethernet to E1 – CARP Streamer

Recorder/Replayers

• 1Mbps to 60Mbps Record/Replay – PC-HSR
• E1 Record/Replay – PC-VDR

Communications Product Map Communications Product Diagram

E1 over USB Data Switching and Capture

E1UC is a new device from Somerdata aimed at the portable acquisition and control of E1 Telecomm data streams for infrastructure management and monitoring in one neat package..

The unit features 4 bi-directional E1 ports that can be switched in any combination, and a grooming port to enable timeslots to be extracted from any of the 4 data ports and routed to a single port for further analysis.

Uniquely, E1UC allows real-time capture and storing of E1 data streams to a host pc via the high speed USB2.0 data port.  Full-rate data from up to 4 streams can simultaneously be recorded to disk or streamed to analysis applications. The USB interface can also be used to perform drop and insert and store/forward operations with a minimum of latency.

Non-volatile storage of set-up allows set-and-forget control from a laptop or handheld device.

Software applications are available for for crosspoint switching, routing, lawful intercept recording and  timeslot grooming and a developer API for .NET is also available., enabling custom applications to be created.

Housed in a smart, high impact resistant case, E1UC measures just 170 x 60 x 30 mm making it ideally suited to field and fast deployment applications with a standard pc laptop.

Typical applications: Switching back-up streams, permanent or temporary re-routing, parallel routing and recording, multiplexing test and creating source streams, lawful intercept grooming, fault back-tracing

E1UC Block Diagram

Click here for a full data sheet and application examples E1UC_Data_Sheet

and here for some applications information

Somerdata Ltd has added 4 channel 1:2 active optical OC-3 and OC-12 splitters to its range of  Communication products.

Aimed at the high-end intercept probe and signal monitoring markets, the units allow multiple 1310 nm OC-3 and OC-12 signals to be split into two paths without degradation. The original signal can be passed through to its destination and a copy sent to other equipment for line quality monitoring,  routing  and probing purposes.

The unit is supplied in a 1U rack-mount configuration with   SC connectors as standard and is part of a range of high-end splitters that will add OC-48 capability this year.
AOS-OC3-124 Data Sheet AOS-OC12-124 Data Sheet

Communications Products

SS-ASR-S Miniature Audio Surveillance Recorder Module

The SS-ASR-S Stereo Audio Surveillance Modules have very small dimensions and weight, long recording times, very low power consumption, wide frequency range (100Hz – 10,000Hz), wide dynamic range and a highly sensitive external microphone.

With the right technical capabilities, the module can be integrated into a variety of everyday objects for covert deployment.

The absence of moving parts means the recorder can function in a wide temperature range, under vibration and in dusty conditions.

It is possible to record by both daily timer and one-off timer.

Recordings are stored in a  proprietary format to prevent unauthorised access and retrieved and managed by attaching the unit to a PC via USB and running the supplied software.  Recordings are then available as   date/time-stamped WAV files.

Data files are signed and can be checked for auditing and anti-tamper purposes.

To secure recorded data, a password may be set which prevents another user from unauthorised access to content and settings.

With up to 24GB flash memory, giving over 5000 hours of continuous recording, the SS-ASR-S Module is one of the most compact and successful recording modules for covert operations.

A range of accessories is available including miniature battery packs, high sensitivity miniature microphones, connector options and wired remote switching.

See also our  Development Kits for a quick way to customise your design for special applications.

Accessories

• External sub-miniature regulator
• High capacity miniature primary power source
• sub-miniature high-sensitivity microphone
• remote switch and indicator

Dimensions

• SS-ASR-S1: 31mm x 25mm x 6mm
• SS-ASR-S3: 45mm x 30mm x 6mm

SSAS Audio Modules Data sheet (pdf)

SSAS Audio Module Record Times (pdf)