NexLink Explained

NexLink is a proprietary protocol for remote-controlling wireless mics developed by Sound Devices. Why does the world need yet another protocol you may ask? This paper will describe why.

There are many wireless protocols from which to choose for controlling transmitters remotely, such as Zigbee, Bluetooth, or Wi-Fi. All of these are excellent technologies for many applications but are not ideally suited for wireless transmitter control. Either the operating range is too short, the power draw is too great, or the link reliability is not solid enough. Of particular interest for sound professionals is a protocol that works reliably, has excellent range, and is legal worldwide. The perfect protocol did not exist, until now. Enter NexLink.

NexLink was written from the ground up by Sound Devices with wireless microphone systems in mind, and achieves what hasn’t been done before: a remote-control protocol which outperforms the range of the audio RF signal by a wide margin without the use of cumbersome repeater devices. You can use NexLink with confidence, knowing that you’ll always be able to control the wireless transmitters from the receiver, no matter how far away the transmitter is from the receiver.

NexLink uses the following technologies to create the ideal remote-control system for wireless mics:

  • Standard, world-wide 2.4GHz spectrum for control
  • Frequency Hopping
  • Special very-long-range, narrow-band, low data-rate modulation
  • Embedded clock for LTC Synchronization
  • Unicast and Multicast messaging
  • Guaranteed message delivery 
  • Simultaneous system operation
  • Diversity operation
  • Full remote power-down and power-up

2.4G Spectrum

The 2.4GHz spectrum is the lowest frequency which is common amongst all countries and license-free around the world. This is the same spectrum used for Wi-Fi, Bluetooth, and many other protocols. We felt this was the best frequency to use for NexLink such that our products can be used anywhere in the world. While 2.4GHz should never be used in professional applications for actual audio transmission due to the amount of interference and associated variability of clean signal available, these issues can be mitigated when 2.4GHz is used for control only. Because of the inverse relationship between antenna size and frequency, 2.4GHz allows for very small antennas to be utilized on both the transmitter and the receiver.

Frequency Hopping

The term “2.4GHz” for the frequency spectrum actually refers to all frequencies within the range of 2.400 GHz to 2.483 GHz, for a total of 83 MHz of bandwidth. Some control schemes require the user to select one channel within this band for the transmit side and the same for the receive side. Not only is this cumbersome to set up, the problem is that if a device (Wi-Fi, etc.) starts transmitting after the channels are selected, the control scheme can quit working reliably. 

NexLink splits the 83 MHz spectrum into over 200 channels for both the transmitter and the receiver. The transmitter and the receiver both automatically hop around different frequencies multiple times per second, following the exact same sequence. In this manner, the NexLink channel is extremely difficult to obstruct, and can find open holes in the spectrum even in the presence of heavy interference. Other than a one-time initial pairing of the transmitter to the receiver (via USB), this is all fully automatic to the user and the user doesn’t have to think about it.

Long-range Modulation

At the heart of NexLink is a proprietary long-range modulation which can operate with negative signal-to-noise ratios. This modulation is, by design, very narrow band and also a very low data rate. It is a well-known principle within RF systems that lower data rate systems can travel over the air farther than high data rate systems. Much like radio systems which communicate with submarines, NexLink uses a very low data rate to go long distances. Because there are relatively few parameters which need to be controlled via remote control, only a few bits of data are needed – and they have to go a long distance. 

Embedded Clock for LTC Sync

When recording on multiple transmitters, it is very important to ensure they are accurately timecode synchronized so that their recordings can be easily synchronized in post production. NexLink was written to embed a very high accuracy clock within the modulation of the signals. Even though the data rate is very low, this allows for extremely precise synchronization of LTC over the air. All that is needed for sub-frame accuracy clock synchronization are very precise clock edges – this is distinctly different from a higher data rate which does not have deterministic edges, like Bluetooth. Previously, various companies have used Bluetooth for LTC sync, but BLE cannot guarantee the sub-frame accuracy of NexLink due to the lack of an embedded clock like NexLink.

Unicast and Multicast Messaging

Unicast means one-to-one messages, and Multicast means one-to-many messages. Some messaging protocols are inherently multicast, sending the same message to all devices. Other systems like Bluetooth are inherently unicast. Using Bluetooth to try and communicate to multiple devices simultaneously can be approximated by sequentially talking to each one-by-one. NexLink combines the best of both worlds and was written from the ground up to be efficient communicating to one transmitter or many transmitters at the same time by using both unicast and multicast messages.

Guaranteed Message Delivery

No matter what wireless protocol or modulation is used, RF travels over the air amongst other RF signals and there always exists the possibility of message corruption. NexLink has two ways of making sure messages arrive. First, each message sent contains Forward Error Correction (FEC). FEC contains extra bits of information sent which auto-corrects any bit-level corruptions which happen. However, above certain amounts of corruption, FEC cannot automatically repair the data. This brings us to the second mechanism: messages retries. If a message gets garbled, this corruption is detected, the message is discarded, and the message gets re-sent and re-tried. This happens automatically without any action needed by the user.

Simultaneous operation

Many simultaneous A20-Nexus receivers can be operated in the presence of one another (each receiver having many associated transmitters). There exists triple-orthogonality between the various A20 receivers. Firstly, the frequency hopping sequence is different for each system. This means that the various systems will avoid using the same frequency channel most of the time. If packets from different systems do collide, then the packet is simply retransmitted again on a different frequency. Secondly, the packets from different systems are addressed using different IDs for all transmitters and receivers, so there is no way for a message to go to the wrong transmitter. Thirdly, the modulation scheme itself is inherently orthogonal from other systems. This is why we say the system is triple-orthogonal or simply ‘can be used at the same time as many other A20 systems without interfering with one another.’

Diversity operation

The concept of diversity (using two or more receive antennas) is not new. This concept has been used on RF receivers for decades to get better reception and thus better range. Diversity is just as effective on the transmit side as the receive side. The A20-Nexus has dual 2.4 GHz transmit antennas, which gives greater range to NexLink.

Full remote power-down and power-up

It is advantageous for the operator to be able to power transmitters totally off and on remotely. Due to the very low quiescent power draw of the NexLink system, the A20-Mini can be remotely turned off or on completely, saving battery life of the transmitter.


NexLink, which has been introduced on the Sound Devices A20-Nexus, contains the sum total of all of the aforementioned technologies. While these may sound great in theory, how does it work in reality? In our real world field testing, NexLink works beautifully, whether at short range or long range, with a quiet 2.4 GHz environment or very crowded. The range of NexLink far exceeds the audio radio link and can be used in any environment to control your wireless transmitters with confidence.

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