This contains details of the weighting curve, meters and a photo of the experimental apparatus and listening room. The temporal weighting is also a decisive magnitude. The work of the C. For instance, when specifying the self-noise of a microphone, the self-noise figure relates to the equivalent sound pressure level in air which would be required to produce such a noise signal in a noise-free microphone. My thanks to an astute engineer named Steve who pointed this out.
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The test requires operating the headphones at their rated input power for a number of hours using clipped pink noise, and muting the noise periodically during the test.
There are plenty of white noise generators around, but this test called for a specific filter and that the signal be clipped such that the ratio of peak voltage to RMS voltage is between 1. More conventionally, we would say that the crest factor is set to 2. Not having a budget for that specialized equipment but having a large stock of components, I opted to make the noise generator myself.
It provides mv P-P clipped pink noise on one output, and white noise and un-clipped pink noise on two other outputs. All of the outputs are connected directly to the outputs of op amps and are not intended to drive long cables or other capacitive loads. The circuit, shown in Figure 1, is composed of a Zener diode white noise source and its bias supply and a preamplifier.
This gets the noise up to the 10 to 20 mv RMS level. A second gain stage provides another 31 db of gain, making the noise signal amplitude sufficient to drive the Pink filter described in EN The filter is followed by another 31 db fixed gain amplifier than an amplifier with adjustable gain, followed by the clipper circuit. The adjustable gain stage is to allow adjustment of ratio of Peak to RMS noise. A transistor switch in the clipper circuit allows muting by shunting the noise signal to ground when biased on.
Several methods of generating noise are discussed on the internet such as this article on this very website. What convinced me was a paper written P. Somlo in in which the suitability of a 6. In his paper, Somlo noted that Zener diodes with a nearly zero temperature coefficient of voltage were also the most stable in terms of noise output as a function of temperature.
The Somlo paper can be read at users. The method of biasing the Zener diode was influenced by Linear Technology Design Note 70 in which Jim Williams described a white noise generator.
As shown in Figure 2, the TL bias supply sets the voltage across the It was noted by Somlo and others that noise as a function of current has a peak followed by a valley, followed by another peak, indicating two distinct modes of operation.
The first peak can be seen in Figure 3 below, in which RMS noise is plotted against voltage from the bias voltage source into the
A Noise Generator per IEC 268-1, IEC 268-5, and IEC 268-7
This design contains a fundamental flaw in that a pink noise filter between the white noise source and the band-shaping filter is missing. The missing filter would go between U2A and U2B. This web page will remain on the internet with this warning since other aspects of the design might be helpful to others. My thanks to an astute engineer named Steve who pointed this out.
IEC 268-1 PDF
Sataur International Consultative Committee of the International Telecommunication Union, Geneva has been unknown to many audio engineers. Within the high-quality studio suite, complications and errors would result iwc, e. IEC 60 is about to be revised to a 4th edition in late or in The C network is used for most measurements, spectrum analysis, peak level indicators, and high intensity sound. I can quote your viewpoint here, or link to it somewhere on the Web. This information led to a fairly clear-cut optimum system, that which the CCIR subsequently adopted unanimously Recommendation Added this Update history section.