well as "full STI" options, the sparse Modulation Transfer Function matrix inherent to STIPA offers no advantages when using the indirect method. Impulse response based STIPA measurements must not be confused with direct STIPA measurements, as the validity of the result still depends on whether or not the channel is linear. List of manufacturers of STI measuring instruments STI measuring instruments are (and have been) made by various manufacturers. Below is a list of brands under which STI measuring instruments have been sold, in alphabetical order. Audio Precision . Offers an STI Plug-in option for use with APx500 Series audio analyzers. Audiomatica . Offers an STI (including STIPA) tool in CLIO 11 system that is compliant with the latest version of the standard (IEC-60268-16 rev. 4). CLIO 12 system is capable of both indirect STI/STIPA and direct STIPA measurements. Bedrock Audio . This is the brand under which Embedded Acoustics sells their STIPA hardware, such as the SM50. Brüel & Kjær . Offers handheld as well as software based solutions. Gold Line . First to offer STIPA measuring solutions (DSP2 and DSP30), but currently not offering any tools that comply with the latest standards (IEC-60268-16 rev. 4). HEAD acoustics . Offers STI options (including STIPA, STITEL, and RASTI) for both the Artemis Suite and ACQUA test systems. Ivie . Offers STIPA-capable acoustic measuring tools such as the IE-45. Norsonic . Norsonic was early to adopt STIPA and offer STIPA modules on their instruments (Nor-140). Sold by Scantek, Inc. in Columbia Maryland. NTi Audio . Offers STIPA modules with their AL1 and XL2 line of acoustic measuring instruments as well as a Talkbox and other peripherals. Apparent market leader at this moment (2013). Quest . Now part of 3M, Quest produces tools such as the Quest Verifier. Svantek Offers an STI (including STIPA) measurement solution with their more advanced sound level meters. TNO. Not currently marketing any products, but sold (among others) the STIDAS series of measuring instruments before. The market for STI measuring solution is still developing, so the above list is subject to change as manufacturers enter or leave the market. The list does not include software producers that produce STI-capable acoustic measuring and simulation software. Mobile apps for STIPA measurements (such as the ones sold by Studio Six Digital and Embedded Acoustics ) are also excluded from the list. See also Mean opinion score References Jacob, K., McManus,