Latency Tab

For supported devices, the Latency tab displays histograms of audio packet latency for each transmitter that the device is subscribed to.

Note:  For video (Dante AV) devices, latency settings made in Dante Controller apply only to the audio channels.

About Latency and Packet Loss

Latency is used to account for the delay between an audio packet leaving the transmitter, traversing the network (potentially through multiple switches) and reaching the receiver.

If a receiver's latency setting is too low, audio packets will not have time to get from the transmitter to the receiver before they are supposed to be played out. When this happens, the receiver will drop packets (i.e. it will throw packets away, because they are 'late to the party').

Packet loss results in audio glitches, so it is very important to ensure that all receivers have their latency set high enough to prevent packet loss.

Setting device latency too high, however, can interfere with low-latency applications (for example, real-time monitoring when recording vocals), so it is sometimes important to find a balance between low latency and guaranteed audio integrity.

The Latency tab can be used to identify:

  • Devices that are dropping packets because their latency is set too low
  • Devices that are at risk of dropping packets because their latency is set too low
  • Devices that could potentially have their latency reduced (if required; generally, the default Dante latency of 1ms is more than adequate for low-latency applications)

About the Histogram

The transmitter's name is displayed at the top of the histogram, along with the latency value against which the histogram is reporting.

The horizontal axis shows the distribution of audio packet latency measurements from the transmitter. The vertical axis shows the number of measurements recorded at each data point, on a logarithmic scale.

Measurements are taken at roughly 1 second intervals, from when Dante Controller is started.

To clear the histogram, click Clear. Latency measuring will then restart.

To save the histogram as a png image, click Save.

Note:  If any subscriptions are via multicast flows, there may be two histograms displayed for one transmitter: one histogram for the unicast flows, and one for multicast. This is because multicast flows always use a latency of 1ms. If the receiver is set to a latency other than 1ms, two histograms will be displayed.

The following information is also displayed:

  • The latency Setting for the histogram. In most cases, this will be the same as the latency setting on the receiver. However, for some subscriptions, Dante will automatically apply a different latency. For example:
  • Multicast flows are automatically set to a minimum of 1ms
  • If a transmitter does not support the latency set on the receiver (i.e. it can't guarantee delivery within the required latency), Dante will increase the latency to the lowest setting supported by the transmitter. Ultimo devices, for example, support a minimum latency of 2ms, so subscriptions to Ultimo devices will use a minimum of 2ms latency.
  • The Peak latency since measuring started
  • The Average latency since measuring started
  • The number of measurements taken that included one or more Late packets (note that each measurement typically includes many packets)

Interpreting the Histogram

If all bars are green and falling well within the limit of the histogram (i.e. towards the left or middle of the histogram), it indicates that the latency setting for the receiver is set high enough to prevent packet loss.

If any bars are amber, it means that some packets are arriving near the limit of the latency setting. Network traffic fluctuations could potentially lead to extra delay which could cause packets to arrive late. A histogram of this type indicates that the receiver latency should be increased if possible.

If any bars are red, it indicates late packets, and audio loss. The receiver latency should be increased, or the network reconfigured.

Note:  Dante Controller can be left running for a few days to collect latency data, providing a long-term picture of the latency performance of your network configuration. This is especially useful after any network infrastructure upgrades, or after the addition of more end point load in a given network, to determine if QoS tuning or increased capacity may be required at the network switch level.