Apple cancelled a high-profile speech at the Jupiter Plug.IN Conference and Expo this week.

The company's vice president of applications and Internet services Eddy Cue was scheduled to deliver a keynote speech at the event in New York. The conference is a key date in the digital music industry, attracting music industry, digital music industry and technology leaders.

Macworld can confirm that the official explanation for Cue's no-show was "sickness". However, sources at the show indicate that most attendees felt that he cancelled as a response to RealNetwork's Harmony announcement Monday.

An unidentified iTunes representative was seen at the event, but has remained reticent to answer questions put by Macworld's sources at the show. Industry gossip claims Apple to have been deluged with phone calls asking its reaction to Real's announcement, and is attempting to formulate a response to that news.

Apple's iPod has so far relied on Apple's own proprietary technology and offered support for the company's own iTunes Music Store. Apple has so far denied overtures from others who hope to make their music outlets compatible with the product.

UK service OD2 expressed interest in working with the company last year, and RealNetworks CEO Rob Glaser wrote to Apple CEO Steve Jobs to open negotiations for some way of working together. These overtures fell on deaf ears.

While Real denies it has engaged in any reverse engineering to develop iPod compatibility for its new technology, analysts believe it's possible Apple will litigate against Real.

Merrill Lynch analyst Steve Milunovich said: "Real could boost demand for the iPod but reduce music store sales," but said he is waiting to see if Apple will sue.