Seems to me that this is FFT basics 101 - interpreting the "grass" seen on an FFT as the noisefloor - in this case -140dB
Have a read of this document in order to understand http://www.ni.com/white-paper/4278/en/ "Computing Noise Level and Power Spectral Density The measurement of noise levels depends on the bandwidth of the measurement. When looking at the noise floor of a power spectrum, you are looking at the narrowband noise level in each FFT bin. Thus, the noise floor of a given power spectrum depends on the f of the spectrum, which is in turn controlled by the sampling rate and number of points. In other words, the noise level at each frequency line reads as if it were measured through a f Hz filter centered at that frequency line. Therefore, for a given sampling rate, doubling the number of points acquired reduces the noise power that appears in each bin by 3 dB. Discrete frequency components theoretically have zero bandwidth and therefore do not scale with the number of points or frequency range of the FFT." What is being shown in the graph is "narrowband noise level in each FFT bin." not the noise floor although the noise floor can be calculated from it given some background information. As to the Regen - it has a good theoretical explanation from John Swenson - the increased electrical noise generated within the USB Phy in handling USB signals with reduced signal integrity. This Regen device seems to address this issue by moving the electrical noise problem off the main USB DAC board into a separate USB hub device. The advantage being that this is USB hub is independently powered & therefore electrical noise can be treated independent to the USB DAC. It then generates a new USB signal with presumably better signal integrity which is meant to be located at the input to the USB DAC. This electrical noise is not quite the same as the 8KHz spike seen in ARchimago's graph which is directly related to 8kHz "packet noise". Archimago's graph, however, does show how electrical noise from internal chip activity can make it to the output. ------------------------------------------------------------------------ jkeny's Profile: http://forums.slimdevices.com/member.php?userid=35192 View this thread: http://forums.slimdevices.com/showthread.php?t=103684 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
