It's often stated that single tone sine-wave tests that are typically used by audio engineers are insufficient to characterize a device under test. The intuitive claim made is that music consists of many tones combined, and so more complex test signals must be used to determine how a device will behave with real music.
Multi-tone frequency response charts are frequently posted, but usually without any quantitative analysis, i.e., measurements. The noise+distortion between the tones is pointed to as something to avoid, but often, it is hard to compare two different devices, unless the noise and distortion are high enough to become very obvious. Some examples from Amir:
AP analyzers and similar measurement devices, often include multi-tone test capability. This is frequently done to get a quick reading, often measuring TD+N (total distortion + noise) or similar characteristic. Because multi-tone signal can be quite short, such a test can be done in a few seconds, unlike the much longer frequency sweeps and other analysis tools normally needed to properly measure a device.
So, my question is.... How useful are the results of a multi-tone test? Does anyone actually post numeric measurements using these? Are such tests in any way better (or, for that matter, different) than single- or two-tone ones? Does the result change with the number of tones? Do we need 3 tones? 32? 64? 100? 1000? And why isn't everyone doing this type of testing, resorting, instead to mostly a single or possibly two-tone test signals? What other useful measurements can be derived from such a multi-tone test? SINAD? THD? IMD? others?
I plan to explore this topic in more detail by running and posting a few tests for discussion, but wanted to hear your experience, thoughts and opinions, first.
Multi-tone frequency response charts are frequently posted, but usually without any quantitative analysis, i.e., measurements. The noise+distortion between the tones is pointed to as something to avoid, but often, it is hard to compare two different devices, unless the noise and distortion are high enough to become very obvious. Some examples from Amir:
AP analyzers and similar measurement devices, often include multi-tone test capability. This is frequently done to get a quick reading, often measuring TD+N (total distortion + noise) or similar characteristic. Because multi-tone signal can be quite short, such a test can be done in a few seconds, unlike the much longer frequency sweeps and other analysis tools normally needed to properly measure a device.
So, my question is.... How useful are the results of a multi-tone test? Does anyone actually post numeric measurements using these? Are such tests in any way better (or, for that matter, different) than single- or two-tone ones? Does the result change with the number of tones? Do we need 3 tones? 32? 64? 100? 1000? And why isn't everyone doing this type of testing, resorting, instead to mostly a single or possibly two-tone test signals? What other useful measurements can be derived from such a multi-tone test? SINAD? THD? IMD? others?
I plan to explore this topic in more detail by running and posting a few tests for discussion, but wanted to hear your experience, thoughts and opinions, first.