What is a Mix-Minus?
A mix-minus is a broadcast term describing the feed sent from the studio to a remote site, so that the remote site can hear the studio output, without hearing itself back. When setting up an IFB mix-minus for remotes, the feed from the studio normally includes a full mix of the studio master mix output (master mix bus), minus incoming audio from the remote site.
Why is a Mix-Minus Required?
Typically, a mix-minus is used by ENG crews, radio and television news reporters and remote trucks, to facilitate live crosses requiring bidirectional communications. Sending a mix-minus feed from the studio allows the remote site to hear studio broadcast audio without hearing the audio from the remote site back on delay. Audio sent via satellite or IP technologies from a remote site has inherent delay on both the transmit and return paths. It is a significant distraction for talent to hear this audio back at the remote site on delay.
As an example, if the IP audio latency between the remote site and the studio is 250ms, and the latency back from the studio is also 250ms, then the round-trip delay is 500ms or half a second. Without a mix minus, remote site announcers hear the full mix back from the studio, including their own audio on delay. This creates an ‘echo effect’ and make it very difficult to maintain broadcasting.
In the early days, a mix-minus was often fed via a telephone hybrid, but increasingly these days it is distributed over IP using devices like smartphone codec apps and audio codecs. Connections over IP nowadays have relatively low latency over robust cellular and broadband data networks. As a result, often the round trip latency over IP is much less than half a second using the latest streaming technologies.
Multiple Live Crosses Require Multiple Mix-Minuses
With multiple simultaneous live crosses it is important to create separate mix-minuses for each remote location. This is usually configured using the studio mixing console. Typically, a separate mix bus will used to send an auxiliary mix-minus feed to each location. This can be tailored for each destination.
Real-World Applications Using Tieline Codecs
Thousands of Tieline customers use mix-minus to facilitate live remotes every day. The Tieline ViA codec allows a bidirectional stereo connection for program, plus a separate mono connection for sending IFB mix-minus communications from the studio. The touchscreen simplifies configuration of IFB signal routing onsite for remotes of any type. This makes it ideal for setting up an IFB mix-minus for remotes.
Configuring Multiple Mix-Minus Feeds
Following is an example of mix-minus configuration for up to six remote sites using Tieline codecs and the Report-IT Enterprise smartphone app. To learn more about Tieline codecs visit www.tieline.com/product.