What technique reduces the bandwidth needed to transmit a signal by eliminating unnecessary information?

The technique that effectively reduces the bandwidth required to transmit a signal by eliminating unnecessary information is compression. Compression involves encoding data to reduce its size, which can involve removing redundant information or using algorithms that reduce the amount of data needed to represent a signal. This process is crucial in various applications, like digital audio and video, where it allows for efficient storage and transmission without significantly sacrificing quality.

By minimizing the data size, compression ensures that less bandwidth is consumed during transmission, leading to faster data transfer rates and more efficient use of resources. This is particularly important in scenarios where bandwidth is limited or costly, as it allows more signals to be transmitted simultaneously or enables higher-quality signals to be sent without requiring additional bandwidth.

In contrast, while techniques like companding, filtering, and controlling have their own purposes in signal processing, they do not primarily focus on reducing bandwidth through the elimination of unnecessary information in the same systematic way as compression does.