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Scientific Measurements vs Real World Usage

This is the kind of thing I was thinking of. I am well aware that all waves can be represented as a sum of sin waves but was wondering what impact the time varying nature of such a sum would have on a DAC and how phase shifting and 'smearing' may only be apparent when such things are considered and measured.
Time and frequency are transforms of each other. If a device has an audio frequency response wider than your hearing, it will reproduce an impulse that will seem instantaneous to you. Something that interferes with timing by "smearing" (which is undefined) or having phase impacts will show up in a frequency response.

Occasionally people argue that a sine wave is "static", so I wrote this recently:
Consider a 1kHz sine wave: sometimes (at the zero crossing point) the voltage is exactly zero, but the rate of voltage change is high, so it sweeps towards the positive rail. It's now a high, positive voltage, but it's soon heading back towards zero. Then it moves quickly towards the negative rail, before diving back to zero. There's nothing static about a sine wave.

And as others have pointed out, Amir does a lot more than use a single 1kHz frequency test. For example, Multitone is a good representation of music, but you can do tests with it, such as noise, frequency response and distortion, which is hard with music.
 
The measurements on this forum seem to be very much about what is produced when an ideal signal is fed in - e.g. a 1KHz sine wave. Its good to have a reference point but what happens when you feed a real musical signal in?

Two things. IMD and masking effects.

Yes, IMD is a real thing, but it's also being tested in the reviews here on the site. So far I haven't seen any indication of it being something worth worrying about.

Masking effects, on the other hand, works in the opposite direction, meaning that the "complexity" of music isn't really doing us any favors in terms of detectability.

The more "musical" a signal gets, the more it covers up the sins of noise and harmonic distortion.

1kHz is really a best-case scenario when talking about detectability. Both because it's a single tone, and because it sits smack in the middel of the most sensitive part of our hearing.

Do different DACs respond differently to different frequency mixes and sudden changes to the frequency content of a signal?

A sudden change is an impulse, and an impulse response is technically the same as a frequency + phase response. If those two show no issues, you're in the clear.

Not to mention that the "sudden changes" that people imagine happens in music isn't anywhere near as sudden as they think.

Even if you want to reproduce the cannon shots of the 1812 overture more realistically, the SPL capabilities of your speakers becomes infinitely more important then the impulse response of your electronics.

For example, are there any tests that have a baseline piece of music that gets fed in and then the output waveform is measured and compared - If you had very similar measuring DACs from the sine wave perspective would they all end up with identical wave forms coming out when actually playing music?

You could try a null tester. I bet all you'll hear is a bit of noise. Probably comparable to a few more insects doing their normal business in the small cavities of your home.
 
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The OP, a new member, asks a newbie question that produces patient, sincere answers that I, a non-scientific person, learned from and appreciated.

Seriously.
I think people see "ah - you test sine waves but what about music" and it triggers people because they've heard idiots talk this way about some magical woo which can't be measured/captured digitally, or is impossible to test. But that not how I read this question. Obviously if a DAC is working properly it'll output the correct analogue signal for the input whether it's a sine wave or merzbow's greatest hits. But that's an ideal DAC; we already know how they work, but this review is about this DAC. It's entirely possible that any DAC under test could have a bad implementation where some combination of channel/frequency/amplitude/phase in some pathological edge case situation (before/after digital silence; where there's intersample overs; a loud/quiet input source etc) produced audible artifacts. If we just look at sine tones and unchanging/simple multitones then this potential edge case is going to get missed.
 
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