Experiments in the BBC led to BBC Research Department Report EL-17, "The Assessment of Noise in Audio Frequency Circuits", in which experiments on numerous test subjects were reported, using a variety of noises ranging from clicks to tone-bursts to pink noise. Subjects were asked to compare these with a 1 kHz tone, and final scores were then compared with measured noise levels using various combinations of weighting filter and quasi-peak detector then in existence (such as those defined in a now discontinued German DIN standard). This led to the CCIR-468 standard which defined a new weighting curve and quasi-peak rectifier.