Sony ACID Pro is a professional digital audio workstation (DAW) software program. It was originally called "ACID pH1" and published by Sonic Foundry, but is now developed and sold by Sony Creative Software.

ACID Pro uses Acid Loops (meaning they contain tempo and key information for proper pitch transposition) painted out across the screen to create music tracks. Acidized loop sample CDs are available from Sony, as well as third party companies.

As with most sophisticated software packages, ACID is not a single software product but defines a family of products spanning a significant range of features. In a related-marketing effort, Sony has continued to support ACIDplanet, a content web site originally launched by Sonic Foundry which is aimed at current ACID users, prospective ACID users and the general public. It describes itself as "the Internet's premier site for music, video and unique artists".

ACID Loops is a technology used with the music making software originally from Sonic Foundry called ACID. Created in 1998, it refers to the repetition, and transposition of sound clips, to form a song. The ACID Pro program is now owned and distributed by Sony, and is on version 7. Sony also now sells a line of Acidized loop sample cds to be used with ACID, as do many third party companies.

An acid (from the Latin acidus/acēre meaning sour) is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger. Chemicals or substances having the property of an acid are said to be acidic.

Common examples of acids include acetic acid (in vinegar), sulfuric acid (used in car batteries), and tartaric acid (used in baking). As these three examples show, acids can be solutions, liquids, or solids. Gases such as hydrogen chloride can be acids as well. Strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid.

There are three common definitions for acids: the Arrhenius definition, the Brønsted-Lowry definition, and the Lewis definition. The Arrhenius definition states that acids are substances which increase the concentration of hydronium ions (H₃O⁺) in solution. The Brønsted-Lowry definition is an expansion: an acid is a substance which can act as a proton donor. Most acids encountered in everyday life are aqueous solutions, or can be dissolved in water, and these two definitions are most relevant. The reason why pHs of acids are less than 7 is that the concentration of hydronium ions is greater than 10⁻⁷moles per liter. Since pH is defined as the negative logarithm of the concentration of hydronium ions, acids thus have pHs of less than 7. By the Brønsted-Lowry definition, any compound which can easily be deprotonated can be considered an acid. Examples include alcohols and amines which contain O-H or N-H fragments.

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