Avid Technology Inc. said it expects to post a loss for the first quarter, a result of weaker demand from amateur musicians and DJs for its products. The Burlington-based company makes equipment for recording music and video. Avid expects a loss of $15 million, including certain charges. It also said revenue was about $152 million, down about 30 percent when compared with the same period a year earlier. That figure missed the average analyst estimate of $161.3 million. Avid is scheduled to release a more detailed report on first-quarter earnings on April 26.