SigmaTel ( SGTL) shares swooned 9% as the company warned of a big sales shortfall.The Austin-based portable music chipmaker says a slow transition to new chipsets and design delays will likely cause a first-quarter loss of 50 cents a share on sales of about $32.5 million. Analysts had been looking for a 9-cent loss on sales of $54.5 million for the quarter ending this week, according to Reuters Research. "Several factors have negatively impacted the company's results for the first quarter," said CEO Ron Edgerton. The company says it made some management changes, including naming Phil Pompa the new head of its portable systems group. SigmaTel shares fell 93 cents to $9.20 in after-hours trading Wednesday.