What is Dante Clocking?

Date Updated: August 1, 2019 FAQ #5888
Question:
What is Dante Clocking and how do I set it up?
Answer:

Introduction to Dante Clocking

Clocking is a critical part of all digital audio systems. Every digital audio device contains a clock, which is used to accurately time out the capture and playback of digital audio samples, much like a metronome helps a musician keep time. When multiple digital audio devices are connected together, they all need to share a common reference to make sure that audio is captured and played back in sync. Dante achieves this using the Precision Time Protocol, which is also known as PTPv1 or IEEE1588-2002.

In a Dante network, one device is assigned the role of Master Clock, and the rest of the devices will synchronize their internal clock to the Master Clock. This device can either be elected automatically by way of the PTP protocol, or it can be manually selected by a user in Dante Controller. This figure shows how Dante systems elect their clock master:

Unless a network has hundreds of devices, any Dante device can serve as the Master Clock without any performance penalty. It's best to select a stable device which is unlikely to be rebooted or turned off as the Master Clock to avoid audio glitches on the network if the Master Clock role is transferred to a new device.

The Master Clock does not need to be synchronized to any particular real-world time source, such as GPS. All that matters is that the device can maintain precise time over long periods, like a good wristwatch does. This ensures that audio is always captured and played back accurately. All Dante devices have dedicated chips on board to handle this task.

How does the Dante Clock relate to Dante Flows?

Each Unicast Dante Flow, or audio stream, consists of four channels of audio. Each UDP packet contains 32 samples of audio for each of the four channels (when there are fewer than four channels, the rest are sent as silence). Each Dante Transmitter embeds the "current" time (per the Master Clock) into each packet of audio it generates. This is the time that the particular packet of audio was captured. Each receiver guarantees a specific amount of latency (usually 1 millisecond), and so with an accurate clock and a packet timestamp, the receiver can play back audio from multiple sources exactly in sync. This buffer can be adjusted in Dante Controller for some devices.

Common Issues with Dante Clocking

The PTP clock protocol relies on Multicast IP traffic to communicate among devices on a Dante network. It also assumes that Ethernet switches will consistently pass the clock packets to their destination immediately upon receiving one. While most unmanaged Ethernet switches handle this task well, some do not. The two most common causes are Energy Efficient Ethernet (IEEE 802.3az, or Green Ethernet), and incorrectly configured Multicast settings.

Be sure that the network switch you purchase for Dante networks is not on our disqualified list. In addition, check the product documentation to ensure that the switch does not have Energy Efficient Ethernet, Green Ethernet, or 802.3az--or that it can be disabled if it does.

If the switch supports configuration, you may need to disable all Multicast Filtering for smaller networks of Dante-only devices. For larger networks or networks with AES67, see FAQ 5423, Dante Networks and IGMP Snooping.

In some cases, it may be necessary to isolate Dante Clock traffic to a small network.