Howdy! This question isn't a request or directed to anyone; it's just food for thought.
Most of the DACs tested in the past couple of years here all show the output of the APx555's 32-tone test signal in the review, which is fantastic because such a test immediately reveals flaws in the digital filter and various nonlinearities in the implementation. However, the test as it is still is pretty static since it only shows the output at one amplitude level. I was wondering if anyone has done this test swept through different levels, a la the SMPTE or CCIF IMD tests.
It'd be really interesting to see how the DACs perform not just at one output level, but at various different output levels. I think such a test would give greater insight into the performance and behavior of the DAC than the simple IMD test which only tests with two tones, and might carry over better to real-world performance since music signals are pretty complex and varied in amplitude. The X-axis can be the peak level of the signal, and the Y-axis can be SINAD - since this is not just a simple wave, the distortion products would include IMD, THD, and other kinds of distortions too. In essence, it's a worst-case scenario of SINAD.
Is such a test complex to do since it would require 32 notch filters, or is it feasible? If it is feasible, has anyone done this kind of test? Which products have been measured that way?
As a follow-up question, what is ASR's standard for measuring IMD? Is it SMPTE, CCIF (or what I call the "Bruno Putzeys IMD test" [Edit: it was actually Bruce Hofer!] with 18.5 kHz + 19.5 kHz), or something else entirely?
Most of the DACs tested in the past couple of years here all show the output of the APx555's 32-tone test signal in the review, which is fantastic because such a test immediately reveals flaws in the digital filter and various nonlinearities in the implementation. However, the test as it is still is pretty static since it only shows the output at one amplitude level. I was wondering if anyone has done this test swept through different levels, a la the SMPTE or CCIF IMD tests.
It'd be really interesting to see how the DACs perform not just at one output level, but at various different output levels. I think such a test would give greater insight into the performance and behavior of the DAC than the simple IMD test which only tests with two tones, and might carry over better to real-world performance since music signals are pretty complex and varied in amplitude. The X-axis can be the peak level of the signal, and the Y-axis can be SINAD - since this is not just a simple wave, the distortion products would include IMD, THD, and other kinds of distortions too. In essence, it's a worst-case scenario of SINAD.
Is such a test complex to do since it would require 32 notch filters, or is it feasible? If it is feasible, has anyone done this kind of test? Which products have been measured that way?
As a follow-up question, what is ASR's standard for measuring IMD? Is it SMPTE, CCIF (or what I call the "
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