Shares of audio chip designer Cirrus Logic (NASDAQ:CRUS) are singing today, jumping as much as 10.1% overnight. The springboard action repaired two days' worth of market damage in one fell swoop:

Charts

CRUS data by YCharts.

Cirrus didn't have any news to drive today's action, and it didn't do anything to deserve last week's punishment, either. But the chart starts to make sense when you add another ingredient to the market soup:

Charts

CRUS data by YCharts.

Cirrus dives 8% when Apple (NASDAQ:AAPL) drops 2%, and jumps right back up when Apple gets a second wind. That's because Apple is far and away Cirrus' largest customer. Every iPod, iPhone, and iPad sold today comes with Cirrus chips driving their speakers and headphone jacks. Cirrus bends over backwards to keep its biggest client happy, and every chip is a custom solution made to Apple's very specific orders.

Cirrus has been looking for secondary revenue streams for years, but Android phones don't reach for high-quality audio because they don't have Apple's ecosystem of music-centric accessories to support. The next big thing on Cirrus' agenda might be LED lighting power management, but LED lamps are still too expensive to really go mainstream. Just ask Cree (NASDAQ:CREE) investors how the LED market is coming along:

Charts

CRUS data by YCharts.

This turns Cirrus into a leveraged proxy for Apple. The businesses and share prices will tend to move in the same direction whenever Apple is in the news, but Cirrus moves faster. The long-term effects of this symbiotic relationship are pretty dramatic:

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CRUS data by YCharts.

Apple has been under heavy fire in recent months. Investors have dropped the stock some 20% from the summer's all-time highs, based on a tasty smoothie of macroeconomic fears, a lack of obvious innovation out of Cupertino, and the magic aura of former CEO Steve Jobs finally fading out. Everyone expects the iPhone 5 and iPad Mini to set sales records in the current holiday quarter, but even all-time blockbuster numbers may not be enough to keep the stock afloat.

That bearish attitude finally took a break today, possibly fueled by hopes of a gentle step down from the onrushing fiscal cliff. If consumers can afford more iGadgets, Apple will prosper. And, by extension, so will Cirrus.

Fool contributor Anders Bylund has no positions in the stocks mentioned above. Check out Anders' bio and holdings or follow him on Twitter and Google+.

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