SINAD of DAC relative to SINAD of HPA @ 50 mv output

[rbinge]

Hello, y’all!
This is my first post on the forum.
I have a background in acoustics, however when it comes to electronics etc., my knowledge is more limited. So, with that said, excuse my ignorance if the following question is practically irrelevant, has already been answered in another thread, or is otherwise based on some misinterpretation on my behalf.

So, the question:
When Amir measures headphone amps one of the measurements is SINAD at 50 mV (and 600 Ohm). As of now, the highest measured SINAD is that of the Topping L30 II (100 dB). I have read that this measurement is one of the more ‘important’ ones, since it indicates noise levels of more sensitive headphones (IEM:s etc) in more practical circumstances. If this is indeed the case, how important is it to have a well performing (Tier 1) DAC with a SINAD of let’s say 120+ dB? The influence of the ‘flaws’ of the DAC on the resulting (50 mV) output signal would in this case be almost negligible, right? Or have I misunderstood something?

Please, feel free to educate me on this matter. Thanks!

 

[RandomEar]

From my understanding: Yes and no. If you're listening at roughly 50 mV, like measured by Amir, even a DAC with a SINAD of 106 dB will only decrease the total SINAD of DAC+HPA to 99 dB, if the latter has a SINAD of 100 dB. If your DAC also had a SINAD of 100 dB, total SINAD would be 97 dB - worse, but still better than an audio CD. You can play with the numbers yourself here (use negative values for SINAD, positive for SPL calculations).

But - there's always a but - you may not be listening at 50 mV. Your typical volume could require more or less voltage, which increases or decreases the current SINAD of your HPA. That may move the current amp SINAD into a territory, where a "bad" DAC at 100 dB could be limiting. If that becomes an audible concern depends on a lot of factors, including your personal "golden eared-ness".

That being said, SINAD on these recent high end DACs is usually noise-limited. Distortion is typically below -130 dB for the usual 1 kHz test. And noise can very easily get audible and annoying when using high efficiency speakers or headphones/IEMs. Therefore, I tend to rather get that DAC with 120 dB SINAD to make sure that noise during otherwise silent passages will never be a concern. But that's certainly a personal preference.

 

[rbinge]

Thanks for your explanatory reply, RandomEar. From what I understand 50 mV is a rather low voltage in this context. Is the case such, generally speaking, that a higher HPA output voltage (> 50 mV) may result I higher/better SINAD? If so, would an HPA with a SINAD of 100 dB @ 50 mV combined with a pair of headphones which require a voltage of >50 mV at listening level, have a SINAD >100 dB (in general)?

BTW, I also tend to go for the higher-rate DAC:s (and amps) simply because I want to keep distortion/noise to a minimum, not necessarily because I fear these would be audible. I mean nowadays, high performing DAC:s/amps don’t need to cost a fortune.

 

[amirm]

As noted, even though I state a SINAD, this is really signal to noise ratio. Increase the signal (volume) and it improves with it. Note also that my analyzer noise is creating a ceiling to how good number can be.

 

[RandomEar]

Is the case such, generally speaking, that a higher HPA output voltage (> 50 mV) may result I higher/better SINAD? If so, would an HPA with a SINAD of 100 dB @ 50 mV combined with a pair of headphones which require a voltage of >50 mV at listening level, have a SINAD >100 dB (in general)?

In general, I would say yes. It depends on the amp, but at 50 mV, I expect most will be noise-limited. Increasing the voltage would then also increase SINAD up to a certain point.

 

[rbinge]

As noted, even though I state a SINAD, this is really signal to noise ratio. Increase the signal (volume) and it improves with it. Note also that my analyzer noise is creating a ceiling to how good number can be.

Thanks @amirm for clarifying this. Also, thanks for doing a great job measuring and reviewing all this tech stuff. An objective viewpoint has really been the missing link when it comes to audio gear reviews.

 

[rbinge]

In general, I would say yes. It depends on the amp, but at 50 mV, I expect most will be noise-limited. Increasing the voltage would then also increase SINAD up to a certain point.

This is pretty much in line with my idea of how these thing ‘work’. Thanks for taking your explaining this.