How is this for a simple summary…
From:
https://www.audiosciencereview.com/...-thresholds-of-amp-and-dac-measurements.5734/
Recap of thresholds of audibility
Lenient
Dynamic range, linearity: 96 dB
THD, IMD: -66 dBFS / 0.05%
Noise: -85 dBFS / 0.005%
SINAD: 85 dB
Frequency response: ±0.5 dB
Channel balance: 1 dB
Strict
Dynamic range, linearity, SINAD: 120 dB
THD, IMD, noise, crosstalk, jitter: -120 dBFS / 0.0001%
Frequency response, channel balance: ±0.1 dB
1) Speakers have a SINAD of 70 or worse. Preference score has been shown to correlate strongly with actual preference. Thus, whenever you have the budget/space/opportunity, upgrading your speaker makes sense. We are nowhere near the limits of audibility.
2) -120 dB is the threshold of audibility. Thus, if you had 130 dB SINAD electronics across the entire chain, you would never be able to upgrade to a system that is more “transparent” to the source. At that point any change in sound that is heard would be the introduction of pleasant coloration. You also would need the frequency and channel matching to be 0.1 dB.
But if we talk about transparent to the source and use lenient thresholds…
1) FM has a dynamic range of 50 dB. Therefore, the most stringent threshold is noise at -85 db and THD at 0.05%. If your integrated amp/receiver had a dynamic range of 85 dB and THD of 0.05% at the volume you need, FM would be entirely transparent to the speaker. Thus, products with 95 dB SINAD would be plenty to ensure full transparency to FM. It’s overkill on the THD but gets you the noise level you want. If you are not sensitive to noise because your listing environment is not quite enough, the THD standards are the limiting factor and once you got to 76 dB SINAD, you probably wouldn’t be able to hear any further differences
with a FM source.
2) Vinyl has a theoretical dynamic range of 70 dB. Most commercial vinyl is below this quality. The same math as FM applies. An electronics chain with SINAD 95 would be fully transparent and if you were insensitive to noise, you’d just need 80 dB SINAD. Again, products with lower SINAD already have crossed the distortion threshold.
Since vinyl has the RIAA curve, errors less than +/- 0.5 dB would be hard to hear but if two phono stages has more than +/- 0.1 dB differences in their RIAA curve, it is possible to hear a difference. RIAA curves can vary greater than 0.5 dB.
The Cambridge Duo measured here is fully transparent to all LPs to the threshold of audibility (lenient). There may be detectable differences in the RIAA curve. In contrast, the Schiit Mani2 has mains noise that might be audible but ignoring noise, frequency response is the main issue. The ability to better match the impedance of the cartridge may give your cartridge a more accurate frequency response. In both cases, upgrading beyond these phono amps is probably not necessary?*
(Headroom to deal with pops may matter, right?)
3) CDs have a theoretical dynamic range of 96 dB. In this case the dynamic range constraint exceeds the other lenient thresholds. If you had a SINAD of 106 dB, your chain would entirely be transparent to the CD.
This then means that once you hit 106 dB SINAD, you are fully transparent. By corollary, a DAC with a SINAD of 90 dB would not be transparent…
Therefore, it is possible (though unlikely) that you would be able to hear a difference between two DACs, if one was 90 dB SINAD and the other was 106 dB SINAD and you were listening to a demo CD that took full advantage of the 16/44.1 format.
4) High res audio is less about the frequency response but more about dynamic range. DSD64 has about 120 dB dynamic range while 24-bit audio has 144 dB dynamic range.
A DSD64 or PCM recorder with SINAD > 106 would capture all of the data that might be encoded in a analog studio master to the thresholds of lenient audibility. A PCM24 recorder would fully be transparent to any analog master tape. Choosing 24/176 would allow the aliasing part to be pushed out far beyond the audible frequency range. The key to going with high resolution is ensuring that the roll off toward 20 kHz remained less than 0.5 dB for the relaxed standard and 0.1 dB for the strict standard.
5) If 130 dB SINAD is needed to be fully transparent to the the threshold of audibility by even the most skilled listeners, you would want 140 dB if applying EQ or room corrrection to stay at 130 across the entire chain.
6) Subjectivists have long said that amps have different sounds, yet ABX testing causes fatigue. Assuming that the amps are transparent in SINAD to the source being used to lenient standards of SINAD, the only explanation that isn’t placebo is:
In reactive loads like a loudspeaker, if the difference in two amps for frequency response exceeds 0.1 dB but is lower than 0.5 dB, the subjectivist could be accurate in that he or she may be able to hear the 0.4 dB over time but have trouble ABX’ing as it would be harder than the lenient thresholds.
7) 18-bits is what Amir reported Meridian stating as the very best dynamic range of real music. We get that this is a rare mastering and would not be representative of most music. That is 108 dB. Therefore hitting SINAD of 118 dB is fully transparent to all known music sampled by Meridian.
8)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4753356/#__ffn_sectitle
This paper suggests that music typically has 60dB dynamic range. Genres with a greater affinity for quiet parts, such as choir, opera, and piano, showed maximum dynamic ranges around 70dB, while “louder” rock, pop, and rap genres tended towards 60dB and below.
In this case, once you hit SINAD of 80 dB, you are probably transparent to most non-audiophile music except for noise which is masked when content is actually being played.
9) Putting this all together, SINAD is critical for identifying how to be 100% transparent to even the most strict standards (shoot for 130 dB) and it’s impressive to see the lack of correlation between performance and price.
The real world experience does support the idea that most DACS and AMPS sound similar since your SINAD threshold for most music is quite low. The audiophile experience does support the idea that audibility can be heard between two good products if one is truly transparent at strict 120 dB SINAD versus ones that are not.
It does seem that we see a lot of variability of amps in frequency response under load when seen at Stereophile.
@amirm, what does it take to test amplifiers with a variety of simulated speaker loads to see the effect on frequency response?