An Explanation of the Inner Works of Wireless Speakers

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This post is mostly designed for people experienced in wireless audio design. You should have a fundamental understanding of how wireless speakers work. You should also know the terms digital audio transmission and digital modulation. I’m going to focus on some methods which were designed to enhance the quality of service of wireless speakers.

Digital audio transmission, as you realize, is much better suited for providing high quality of service then FM transmission. The data which is being transmitted instead of the role audio, can be repaired inside the speakers. That process is called forward error correction. This type of error correction is usually used for points-to-multipoint transmission systems. In that case, the receiver usually does not have the way to talk back to the transmitter. Therefore, the transmitter when preparing the data for transmission, adds redundant information. Simply adding a checksum is not enough. A checksum simply would allow the receiver to detect errors and mutes the audio. It would not allow the receiver, however, to repair any damage.

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For the above reason, modern wireless speakers typically add redundant information to the data stream. This redundant information will increase the data rate that is being transmitted. The receiver uses this additional redundant data recover missing or corrupt data which was damaged by interference. In addition to interference, multipath fading is also a major problem in wireless audio transmission. This phenomenon causes the notches or fluctuations in signal strength in different areas. This not only happens if the speaker was to be moved throughout the room but also if some person was to move in relation to the speaker thus causing the signal components to shift.

Forward error correction can only recover data to certain extent. Usually short bursts of errors can be corrected. However, in some cases forward error correction is not able to repair the data fully. For that reason, a checksum is also added into the data stream. That checksum will verify to the speaker whether the data is correct or not. If after applying the error correction, the data is still not correct, the audio is usually muted by the speakers.

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Four point-to-point transmission systems, on the other hand, usually bilateral data transmission is employed. That means that the speakers will be able to talk back to the transmitter. That allows the receiver to indicate to the transmitter that any package of data has been lost or corrupted. Therefore the transmitter can re-sense that missing or corrupted data packets to the receiver. However, keep in mind that in order for this to work, there has to be some amount of data buffering. That by definition causes a certain latency or audio delay which must be compensated if some speakers are wireless wells are the speakers are wired directly.