This is definitely a sidetrack, so pardon the interruption.
I did say that THD+N, SNR, Crosstalk, etc., have been measured for many years. And we've been talking about them for many years.
And SINAD is the inverse (alternate term) for THD+N. But WHY use it in the first place when it's just an ALTERNATE term? Does it ADD any more useful information?
Why not just continue using THD+N since it's been used since FOREVER?
With that out of the way and back to the fact that we've been talking about THD+N for many years now, it seems like THD+N has always been good to discuss, but not
OVEREMPHASIZED over Power Output or other specs. Back then, THD+N was just "one of the guys", sort to speak.
With all these THD+N numbers being inaudible, why make such a big fuss over them?
You are right, there is no reason to use that term, but could be one, if you use the log scale. We all know why in audio it is better to use log (the natural log) scale.
In communication though, that's where the term would be used, but for reasons, you would have to ask
@gene who was a communication (telecom..) engineer, for me I only study communication theory in U, never practice in that discipline though I know I would have enjoyed it more, than in the world of power electronics, power T&M, and control that I spent my whole career on.
By definition, THD+N could have been expressed as NADIS
, that is noise and distortion/signal, and either way, the number in dB would obviously be negative because log(1/X) = - log(X)
I believe the I, is actually evolved from the "/" sign that is the division sign,
If the ratio is 1/100, that is 1% then THD+N = 20*log(1/100) = -40 dB
SINAD, will of course = +40 dB but the + sign is not used, as it is implied.
So if you prefer a positive number, you are saying the signal is 40 dB stronger than the distortions + noise, or if you prefer a negative number then you are saying the magnitude of the distortions + noise is 40 dB lower than the signal.
I prefer THD+N, but in dB. It seems that DAC manufacturers typically use THD+N as well. I have seen it expressed in SINAD only in AKM's ADC, such as the one used in D+M's and Yamaha's:
Example, the AK5358
S/(N+D): 92dB
Note they use the "/" sign instead of the "I", to me that should have been the right way.
I prefer THD+N expressed as dB because it is easier to relate it's practical meaning, as we know 0 dB, or -100 dB from the fundamental of a signal that is at 100 dB is probably inaudible, or barely perceivable to most people so if the total harmonic components plus noise is at -100 dB that is 100 dB below a 100 dB signal, then I won't be able to hear it even during the quietest passage of music such as in between tracks. If it is in %, such as 1%, then it is harder to imagine in terms of audibility without converting it to dB.