two, with a significant delay added to the analog service. In some cases, particularly during tropospheric ducting events, an HD receiver will lock on to the digital stream of a distant station even though there is a much stronger local analog-only station on the same frequency. With no automatic identification of the station on the analog signal, there is no way for the receiver to recognize that there is no correlation between the two. The listener can possibly turn HD reception off (to listen to the local station, or avoid random flipping between the two stations), or listen to the distant stations and try to get a station ID. Although the signals may be synchronized at the transmitter and reach the receiving equipment simultaneously, what the listener hears through an HD unit and an analog radio played together can be distinctly unsynchronized. This is because all analog receivers process analog signals faster than digital radios can process digital signals. The digital processing of analog signals in an HD Radio also delays them. The resulting unmistakable "reverb" or echo effect from playing digital and analog radios in the same room or house, tuned to the same station, can be annoying. It is more noticeable with simple voice transmission than with complex musical program content. Stations can transmit HD through their existing antennas using a diplexer, as on AM, or are permitted by the FCC to use a separate antenna at the same general location, or at a site licensed as an analog auxiliary, provided it is within a certain distance and height referenced to the main analog signal. The limitation assures that the two transmissions have nearly the same broadcast range, and that they maintain the proper ratio of signal strength to each other so as not to cause destructive interference at any given location where they may be received. Artist Experience HD Radio supports a service called "Artist Experience" in which the transmission of album art, logos, and other graphics can be displayed on the receiver. Album art and logos are displayed at the station's discretion, and require extra equipment. An HD Radio manufacturer should pass the iBiquity certification, which includes displaying the artwork properly. EAS alerts Since 2016, newer HD Radios support Bluetooth and Emergency Alert System (EAS) alerts in which the transmission of traffic, weather alerts, AMBER, and security alerts can be displayed on the radio. As with