Abstract: A method and apparatus are disclosed primarily for measuring the linear density of a sliver of fibrous strands (e.g. textile) as they are drawn through a trumpet on a processing machine. The measurement is made by detecting the naturally occurring acoustic emissions or signals generated by the frictional and compressive forces between the fibers and between the fibers and the wall of the trumpet as the sliver is drawn through the trumpet. The intensity of the acoustically emitted signal is proportional to the density of the sliver passing through the trumpet. These acoustic emissions are detected by a microphone which convert the acoustic signals to an electronic signal which is amplified and electronically processed to indicate the density of the sliver and may be used to control the textile machine and furnish diagnostic data.