Can we talk Input sensitivity and signal to noise?

[jamiecantar]

Once and a while I visit Hifi-engine to read up on spec's of an interesting piece of kit I may be interested in. I notice that from one receiver, integrated or amplifier to another the line level input or sensitivity can be different, such as one may have 150mV (line) another 300mV (line) and also the Signal to noise ratio db's can be different on the rca plugs, like one cd input can produce 96 db and another unit can output 112dB (line)...

my question is, the higher the number the better the sound at low volumes? or what?

can someone shed some light?

thanks

 

[the skipper]

as for the sensitivity, that's the input voltage required for the amp to be driven to it's rated output.

S/N is a reflection of how far the noise level is below the sound you hear. the higher the number, the better. https://en.wikipedia.org/wiki/Signal-to-noise_ratio

 

[Rdenney]

Signal/noise is a ratio, in dB (or percent). At low volumes, you do not need a high signal/noise ratio, because even with a low ratio, the noise floor will still be masked by ambient room noise.

Let's say you have a system with a signal/noise ratio of 100 dB (or 0.001%). Let's say your listening room is quiet but typical, with an ambient noise level of 35 dB sound pressure level (which is an absolute scale). If you keep the noise floor of your system 10 dB below that, you'll never hear the noise products, which will be reproduced at 25 dB SPL. That means your amp would have to produce peaks at 125 dB SPL for the noise to become audible. Your amp and speakers probably can't do that, and you wouldn't be able to be in the same house with it if it could.

We reward good engineering that shows high levels of transparency, but I think most people would struggle to gain any advantage from amps with signal/noise higher than 80 dB or so, even if they listen quite loudly.

Input sensitivity just tells you want voltage you need from your devices or preamp to drive the amplifier to full power.

Rick "we overestimate what we need in some measures and underestimate others" Denney

 

[lini]

jc: Well, basically a high input sensitivity is desirable, if one has sources with pretty low output level or respectively recordings with pretty low recording level. And why a high signal-to-noise ratio is desirable, should be obvious anyway.

However, in case of both one needs to be careful, that one keeps the conditions in mind, in order not to compare apples and oranges. In case of pre-amps that would be the rated output voltage, in case of receivers, integrated amps and power-amps usually the rated output power. Or in other words, one needs to heed, which output voltage or which output power the input sensitivty and SNR values refer to. For example, on paper quite a few older German receivers, integrated amps and power-amps might look rather bad in terms of SNR, but that's simply due to their SNR values not referring to full RMS output power, but just to an output power of 50 mW instead. And similarly, it's also not that much of a suprise, that a comparatively low-powered receiver, integrated amp or power-amp typically won't reach as high SNR values as a high-powered model, despite being just as noise-free in practice, simply due to the difference in output voltage and power.

Greetings from Munich!

Manfred / lini

 

[toddalin]

Signal/noise is a ratio, in dB (or percent). At low volumes, you do not need a high signal/noise ratio, because even with a low ratio, the noise floor will still be masked by ambient room noise.

Can't agree from actual experience. The lower the volume, the more important the S/N becomes because you don't have the loud signal to cover it up.

Recognize that in all equipment there is an inherent noise floor even at it's minimum volume. This floor becomes more apparent as the volume level is decreased.

I had a Yamaha 31-band eq in my system, and could hear the hiss when nothing was playing. By definition, the hiss is noise. It was covered when music was playing, but I could not tolerate it between tracks.

 

[Rdenney]

Can't agree from actual experience. The lower the volume, the more important the S/N becomes because you don't have the loud signal to cover it up.

Recognize that in all equipment there is an inherent noise floor even at it's minimum volume. This floor becomes more apparent as the volume level is decreased.

I had a Yamaha 31-band eq in my system, and could hear the hiss when nothing was playing. By definition, the hiss is noise. It was covered when music was playing, but I could not tolerate it between tracks.

The point is that below the audibility floor, noise doesn't matter, and this is especially true for quiescent hiss. If that hiss level is below the noise floor of the listening environment, making it lower won't have any audible effect. I have a quiescent hiss from my B&K amps that requires me to be about two feet from the tweeter to hear. It's the only thing that bothers me about those amps. Yes, they are power amps with no volume controls, so this is probably their own self-generated noise playing at full volume, and the only music level at which it is at all audible is zero. I expect it's about 80 dB down, but I haven't measured it.

And I also have a Yamaha equalizer, a very nice parametric equalizer from a couple of decades ago. It adds maybe 3 dB to that quiescent hiss--enough to hear that it has been added. So, I know of what you speak. But what would make those base hiss levels inaudible is keeping them below a certain threshold. I have not measured the voltage of that hiss at my speakers, though I really should, but the newest amps have a very low quiescent hiss in the sub 40 microvolt range. (I wish this was consistently disclosed and tested.) That is not the only noise in the S/N, but I agree it counts.

But if that hiss was at 25 dB SPL in my living room, I doubt I'd be able to hear it at all. Let's say that's where it is. And let's say it's self-generated by a power amp downstream of where the signal is attenuated (as with amps that have no level control, which mine don't), so the hiss is absolute. If my peak music signal was at 60 dB (not very loud but not soft, either), the ratio over that hiss would be 35 dB. If I'm playing peaks at 120 dB, the ratio over that hiss would be 95 dB. For an amp that can produce 120 dB SPL with my speakers, and is controlled by upstream preamps, I'd want a S/N of 100 dB over that quiescent hiss. That's not that unusual these days. But the ratio will be lower when the signal going into that amp is attenuated.

Rick "noting the downward slope in all distortion/noise vs. power plots until distortion becomes the controlling defect" Denney

 

[jamiecantar]

In one of my set ups I use a 1989 JVC AX-Z1010tn integrated amp. the spec's are:
Input sensitivity: 0.3mV (MC), 4mV (MM), 300mV (line)
Signal to noise ratio: 71dB (MC), 89dB (MM), 112dB (line)

Then I have another: A 1966 Mcintosh MA-5100 integrated amp and the spec's are:
Input sensitivity: 2mV (MM), 300mV (line)
Signal to noise ratio: 70dB (MM), 75dB (line)
Output: 300mV (line)

You can see that the Mcintosh has a lower Signal to noise ratio using a Moving Magnet cartridge on the phono stage, but with the JVC on my turntable I use a Shure M44-E with an Output voltage: of 9.5 mV per channel.
and I have to say the combo output volume is amazing, I don't know if 4mV on the phono stage is good? but I'm getting some sweet output volumes with this combo...

Although I'm wondering if I use the AUX output with a separate external phono stage would I get better results using the Mcintosh because the line is 300mV output?...or will the external phono stage merely squash the output back down?

Reason I ask, on occasion I play some 1950's and 60's classical and opera records that were engineered at very low volumes, and when I open the volume Im just increasing tape hiss and other noise...or is it, what it is? What's the best stylus/cartridge and gear combo for playing low volume classical and opera records?

 

[JoeESP9]

You guys gotta realize that most users wouldn't even know what you were talking about if you told them to jumper the connections to the switch. Heck the guy was probably lucky to understand that screwing that block of wood on there to hold the switch button in would keep it on.

Doug

Can't agree from actual experience. The lower the volume, the more important the S/N becomes because you don't have the loud signal to cover it up.

Recognize that in all equipment there is an inherent noise floor even at it's minimum volume. This floor becomes more apparent as the volume level is decreased.

I had a Yamaha 31-band eq in my system, and could hear the hiss when nothing was playing. By definition, the hiss is noise. It was covered when music was playing, but I could not tolerate it between tracks.

Was the hiss audible if the equalizer was set to flat?

 

[lini]

Jamie: Well, your MA-5100 should have a phono stage gain of 300 mV / 4 mV = factor 75 or respectively ca. 37.5 dB. So with any phono stage with a lower gain than that the output level would be lower.

Well, and regarding the SNR values of the JVC compared to the SNR values of the McIntosh, one would first have to properly study the specifications - 'cause what I've mentioned in my first reply above, aren't the only things to heed for a proper comparison (or at least for checking, whether it's a proper comparison). Another thing would be the type of SNR, namely unweighted/linear (over here in Germany: Fremdspannungsabstand) vs. weighted/with a filter, that's supposed to mimic the human hearing sensitivity curve (in Germany: Geräuschspannungsabstand). And then there also is the exact measurement standard or respectively the (corresponding) "fine print". For example, an MM phono stage could be either measured with an actual, typical MM or MI cartridge connected or rather with a generated test signal (most typically 5 mV, but I've also already seen some specs given for a 10 mV test signal...) for the reference level and with the inputs shorted to ground for the noise level. And of course the manufacturers often enough merely refer to the standards, which for most of us hifi fans aren't accessible for free... So, all in all, proper spec comparisons often aren't easy.

Greetings from Munich!

Manfred / lini

 

[toddalin]

Was the hiss audible if the equalizer was set to flat?

Yes. I actually made a 10 dB attenuation cord for it by installing resistors within the RCA plugs.

Recognize this is through JBL L300s so the speakers are quite efficient.

 

[sqlsavior]

The point is not whether or not you can hear the noise distinctly, or whether it is "covered up". The point is that it pollutes the signal, and interferes with clarity. Any fixed amount of noise is worse at low volume, as the s/n ratio decreases.

 

[twiiii]

It all depends on how many links you have in the chain between the source and the speakers. I deally you would be operating all the pieces around 10 db below recommended levels and the adjust the amps for the levels you prefer for best signal to noise and satisfactory very low distortion. But you can't do that with consumer equipment it takes some one with brains to set up a system that way and a lot of stereo components just don't have the capability in the execution of their designs. So if you have an integrated unit you are pretty much stuck. Your only hope is the source has an output control so you can operate your system with the volume control around the 12:00 position and then adjust the CD player or tuner or tape machine for optimal results. Of course if you have a TT then you have to select the cartridge with the out put level that matches your likes.

Your better units have internal level adjustments for each input to get the desired results with in an optimal range. Two or 3 db can make quite a difference. Back in the days before noise reduction when tape machine had about 55 db signal to noise we would set the levels in a very quiet room to where the tape hiss could be barely heard and then play the tapes. If a room had a nose floor of 30 db then the maximum output would be around 85 db which is normal for most serious consumer listeners. Where professionals might prefer 90 db. Of course there is always the issue of peaks. Pop recordings are about 6 to 7 db, but everything else can vary all over the place. I have classical stuff that can easily approach 70 db variations all the time. Telarc and Reference recordings will go even higher than that some times.

I set my HT system for peaks to reach 96 db loud sound effects. Home stereo about 85 db, unless I am playing pieces with very wide dynamic range and then I'll let the system reach concert hall peak levels of 104 db maybe for a few peaks in an hour or two recording. That requires about 120 watts for each channel working to gether. I have 600 watts per channel. That gives me 8 db of spare hed room before the power Guard kicks in limiting the output. My Apple watch keeps track of my exposures to loud levels. And most days its around 100 db. But that exposure if from things like car door slams tail gate closures on pickups, maybe pounding a hammer or the lawn mower. If I let the sound levels get to strong one of my apps will worn me either on my Apple iPhone or iWatch.