Measuring a portable audio device’s response to excessive sound levels

Kendrick, P; Cox, TJ; Fazenda, BM; Jackson, IR

Abstract

This is a report detailing how a series of measurements were carried out to quantify the non-linear performance of a series of portable audio recorders. The performance of a series of common devices is quantified including the; Cannon 550D, Edirol r44, Neumann U87ai via Focusrite 2i4, Shure SM57 via Focusrite 2i4, Zoom H2, Zoom H4, Google Nexus 4, Apple Iphone and a Sony camcorder (vx2000). Parameters relating to attack release and thresholds of any dynamics processing present are reported, and the devices are probed for any non-linear behaviour such as clipping, if any non-linear behaviour is identified it is parameterised by extracting the gain curve which relates input level to output level.
Most devices have some form of dynamic gain control to prevent signal clipping, but the implementations clearly differ considerably. Some devices have many options and setting for different situations indicting that there is no one particular method suitable for all cases. The attack and release times of the measured systems range from 5 to 17 ms and 30 and 400 ms respectively. Some devices may also demonstrate a nonlinear gain curve with no attack or release but which try to limit audible distortion by using a compression ratio of between 1.4 and 10. While other systems have no protection and when presented with excessive sound levels will exhibit hard clipping.

Citation

Kendrick, P., Cox, T., Fazenda, B., & Jackson, I. Measuring a portable audio device’s response to excessive sound levels

• Report Type: Technical Report
• Deposit Date: Jul 9, 2013
• Publicly Available Date: Jul 9, 2013
• Publisher URL: http://www.goodrecording.net/
• Related Public URLs: http://www.goodrecording.net/distortion/
• Additional Information: Funders : Engineering and Physical Sciences Research Council (EPSRC)