The Riverside Co. has bought a majority stake in Spectrio LLC, an audio and video marketing company, for an undisclosed price.

The sale of Oldsmar, Florida-based Spectrio marks an exit for SJ Partners LLC, a private equity firm based in New York. SJ first invested in Spectrio in 2005 when the portfolio company did business as Audio Messaging Solutions. Since then, SJ completed fourteen add-on acquisitions: AdTel Group LLC, Audio Marketing Systems Inc., Audiomax, Focuspoint Inc., Hold It Systems Inc., HoldPlus Inc., Sonic River Studios Inc., Broadcast Marketing & Entertainment LLC, Perception Marketing LLC, Performance Audio Marketing, Phone on Hold Marketing Systems Inc., Profit-Tell International Inc. and Vericom Inc.

BMO Financial Group, NXT Capital and New Canaan provided financing for the transaction, while Lazard Middle Market advised Spectrio on the sale process.

Cleveland and New York-based Riverside focuses on buying an investing in businesses that are valued at up to $250 million. The transaction underscores the continuous dealmaking on the part of Riverside. In September, the firm bought Protexer, a company that makes and sells shoe covers, followed by Medical Payment Exchange Inc. 

Also in September, the firm invested in Tate's Bake Shop Inc., which makes cookies and baked goods. In August, the firm backed craft beer brewery Uinta Brewing Co. The firm's co-CEOs won Mergers & Acquisitions M&A Mid-Market Dealmakers of the Year award for 2013.