The Audio Science Review Forum

Why isn't the acronym SNAD?

Thought I'd best do my homework by looking at the two pages in the APx500 users manual - that's two pages out of more than 500!

S/NAD - signal to noise and distortion - now called SINAD, is the reciprocal of THD+N (1/THD+N) and the unit is dB (the decibel).

It's related to ENOB (hahah) - Equivalent Number Of Bits.

120dB S/NAD is 20 bit. 20 bits containing 6dB of audio information = 120dB.

Never heard of 20 bit? It's known as 24 bit. Four of the 24 are non-audio bits for something else. I guess 24 looks a lot larger than 16, whereas 20 might not?

But S/NAD was intended as a quick "all in one" test for radio communications - where there is a lot of noise and distortion - to give an indication of clarity.

There is no SINE in S/NAD, so why they have to show the sine wave so large, when all we in test know the stimulus is a sine wave anyway, I don't know.

The other display is the FFT (used to be called a spectrum analyser), and if you shorten the FFT (reduce the resolution) can look quite phallic! NADs and NOBs, hey!

Getting that low in the digital domain is easy - just select the right chip. But getting that low in analogue means trading off "speed" (or slew rate) to slow down the Brownian motion, to reduce the noise. But then, just use an enhanced slew-rate op-amp to boast ultra-fast slew.

So, does that sound natural? DIF! So what sounds natural? Well, a natural slew rate of course! And how do you obtain a natural slew rate? By trading off some of the noise! But that won't do 120dB... 

Exactly!

I saw this video more as comment on the use of measurements as the only method of reviewing,  scoring and comparing products rather than actually listening.  That when viewing these reviews you cannot not make accurate judgements when you see these test figures as you would not know all the settings used in the testing never mind whether they are relevant or not. This chimed with your previous comment about methodology  testing of phono stages used in a phono stage review on the ASR site.

While the almost mythical SINAD figures quoted by some far east dac makers, and praised as a target by at least one magazine and particular reviewer (120dB or nothing) and some youtube review channels, is the subject of several youtube videos I felt the the comment about manufacturers in this video was more a question of 'BBC' balance and was not expecting it would imply a required response so I will be more careful with the links next time as this was certainly not my intention.

There is another video by the Headphone show if you search for SINAD on youtube discussing the fruitlessness of judging a product based on a single value as used by some review sites/channels.