By selling stocks down last week — the Dow finished down 1.9 percent, the S&P 500 lost 2.5 percent and the Nasdaq fell 2.3 percent — investors may have signaled that they're now more pessimistic about companies' reports. But they may be still be more optimistic than earnings data and outlooks will justify.

"This is going to be a very challenging earnings season," said Jill Evans, co-portfolio manager of the Alpine Dynamic Dividend Fund. "In March, things were so dire. No number was too bad because expectations were so low."

In addition to Alcoa's numbers on Wednesday, investors will get reports from the Institute for Supply Management on the services sector during June and from the Commerce Department on last month's retail sales and wholesale inventories. A preliminary reading on consumer sentiment in July from the University of Michigan will be issued on Friday.

The report on wholesale inventories especially will be looked at closely, analysts said.

"Low inventories now mean future growth later," Evans said. "It will be interesting to see if those numbers continue to show low, lean, managed inventories."