Is Your System's Noise Floor Low Enough? - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 59 Old 12-10-15, 03:54 PM Thread Starter
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Is Your System's Noise Floor Low Enough?

The funnest discoveries are the surprises. Like setting up a pair of speakers and accidentally getting a monster soundstage. Like discovering that the openness of a soundstage can be affected by a system noise floor level that you can not even hear when no music is playing.

The latter example is what I ran across in just the last couple of weeks, and it has been great fun figuring out what is going on and how to improve it and hearing the resulting improvement.

Some history:

My laboratory is divided into two areas, and the Music Server is in one area while the Receiver and Speakers are in the other, the listening area. The power all comes from one set of outlets from a single breaker. A Uninterruptible Power Supply (UPS) powers the Server and provides surge and noise protection for all the rest.

A couple of years ago I realized there was a noise floor problem - quite a bad one - with the line-level signals running from the Music Server's Audio Interface to the Receiver, a stereo pair of 15-foot RCA-to-RCA cables. It was bad enough that I could just hear the noise at the LP at higher listening volume settings with no music running. At normal volume level settings, I could hear it when I moved close the the speaker. It was mostly hiss with a little bit of 60 Hz hum. I had tolerated it for a couple of months while I selected and ordered some TOSLINK optical cables and a powered TOSLINK selector/splitter.

When I got those parts and set them up and switched over to TOSLINK, I was completely blown away by the difference. Of course the noise when the music was not playing went away. But the bigger benefit was that the openness of the soundstage was transformed. The areas between sound images in the soundstage went from cloudy dark to deepest black sonically. The difference was striking.

The lesson was that, although I could not hear the noise directly when listening at any level with music running, I could perceive that it was there in the lack of clarity and openness of the soundstage. I went back and forth numerous times between configurations to verify that I was not imagining the effect. Obviously, the RCA cables were ditched and it has been optical ever since. Until......

Current System configuration:

Is Your System's Noise Floor Low Enough?-syscfg-sm.jpg

The diagram shows my current system configuration, which has evolved over time. It is worth noting that at the time I configured Dirac Live in both of the DL devices, there was project file compatibility between the two versions (miniDSP nanoAVR DL and Dirac Live PC Full), and the same set of measurements was used to generate the DL filters in the two devices. (This is no longer possible.)

Most of my serious listening has been done from the music server, with the Bluray being used mainly for movies.

Recent Discovery:

The Bluray has USB ports on front and back. The documentation does not say so, but I wondered if it might work with a regular NTFS-formatted hard drive, so I pulled my external music backup drive over there and plugged it in and sure enough it worked! Cool! I pulled up an album to listen to. It was one I had not sat through for a year or so, so I relaxed and enjoyed it very much and was impressed by the openness and clarity of the mix and soundstage.

Then on a whim, I decided to play the same album from the music server, mainly to be comparing the nanoAVR DL version of Dirac to the full PC version, expecting the PC version to be a little better somehow. What I heard bothered me more than a little, it just did not sound as clear, and it seemed like it should be at least as good, if not a little better. I went back and forth a few times using different tracks from that album, and, sure enough, the Music Server sound was not as open and clear as that from the Bluray.

I was aware that the level settings in Dirac can be a little different between the two versions, so I was compensating for that with AVR volume while switching back and forth.

Then I got to wondering about the optical signal from the Music Server, which I had not used for awhile since getting 5.1 running via HDMI from the Server. So I switched over to the TOSLINK.

ZOWIE! The clarity and openness were back! It had nothing to do with Dirac, it was a noise floor problem running the HDMI from the Server over to the AVR. I verified it by cranking AVR volume to max (being very careful!!!) with streaming but with no music running, and switching from HDMI to HDMI to TOSLINK. With my ear up to the speaker, I could hear hiss using the HDMI from the Server, but not using the HDMI from the Bluray/nanoAVR-DL or the TOSLINK from the Server. The noise floor was high enough using the HDMI from the Server to cloud up the soundstage even though I could hear no noise at the LP even at higher volume settings.

Measurements:

I VERY CAREFULLY took these noise floor measurements using the balanced mic input of my audio interface connected to the Main Left speaker output of the Power Amp. I made sure that streaming was taking place for the measurements. After compensating for a smalL gain difference, the noise floor difference is 10 dB. The noise profile is equivalent to white noise. When playing music using the HDMI signal from the Server, the system has 10 dB more noise than when playing music from the Bluray/nanoAVR-DL HDMI input or the Server TOSLINK input.

measurements to be added shortly...

An Experiment:

Then I created an experiment. Using Reaper, I took a track and made a bunch of versions of it with different amounts of white noise added. I was able to verify that it is possible to perceive the clouding of the soundstage even though I can not hear noise before the music of the track begins. I am going to try to set up a download point where HTS members can download noisy versions of a segment of that track without the amounts of noise identified (a semi-blind test) and a survey to see at what levels HTS members can detect clouding of the soundstage. I am also going to get Tesseract over to see what he hears.

Definitions:

All of the signals discussed are digital. The only analog conversion takes place in the AVR. The noise is not being added to the digital signal. The noise is entering the AVR, probably because of a ground loop - the room is not kind to ground loops - depending on what input is selected. I will be digging into the cause further.

THE LESSON:

Check your noise floor! With no music running, and with streaming taking place, CAREFULLY crank up your volume level and see what you can hear at the LP and next to your tweeter.

CAUTION - CAUTION - CAUTION - CAUTION - CAUTION - CAUTION - CAUTION - CAUTION - CAUTION
Turn your volume setting down to normal or below before selecting a different source or making ANY change to your AVR settings or anywhere else in your system. Then turn it back up after that change has been made to hear the result.
CAUTION - CAUTION - CAUTION - CAUTION - CAUTION - CAUTION - CAUTION - CAUTION - CAUTION
  • If you hear noise at the LP with a normal listening level, your soundstage is seriously compromised.
  • If you hear noise at the LP with volume at max, or at the tweeter with a normal volume setting, your soundstage is probably somewhat compromised.
  • If you hear noise at the tweeter with volume at max, your soundstage might be somewhat compromised.

What to do if you have a problem:

More investigating and posting to follow...


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post #2 of 59 Old 12-10-15, 05:35 PM
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Re: Is Your System's Noise Floor Low Enough?

Good call Craver, and this is not a well thought about phenomena in this hobby. Any noise being introduced into the system, either electrically or mechanically will most likely be detrimental to the listening experience.

I cannot guess what your noise is as it might be something as easy as a cable or signal from the server through that loop. Using a toslink seems to be the best way to go as it does not involve the possibility of ground loops or other contamination, whilst an HDMI cable should be silent, I too have run into some issues. I would recommend a toslink cable first, then a coax cable then USB and finally hdmi. This is just my opinion of course based upon my system. I use my server with toslink into my DAC and then good interconnects from the DAC to the AVR. Not only is it quiet but I get a pretty substantial amount of dynamic range because it is so quiet.
Dynamic Range in any given room may be another good discussion.

Good Listening

Jack

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post #3 of 59 Old 12-10-15, 09:54 PM Thread Starter
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Wayne Myers
 
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Thank you for the feedback. There is still much to figure out.

For instance, these differences were observed by simply switching selection of input, not by removing any path that could be a noise path. The?noisy HDMI path was still there, just not selected.

Some careful diagnosis is certainly in order.

I want to be able to play 5.1 from the music server also. So I need to quiet the HDMI path.


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post #4 of 59 Old 12-10-15, 10:40 PM
 
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Re: Is Your System's Noise Floor Low Enough?

I am always wondering if I am losing any info from the noise floor...subscribed to see what you turn up.

Ron

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post #5 of 59 Old 12-11-15, 07:51 AM
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Re: Is Your System's Noise Floor Low Enough?

Quote:
AudiocRaver wrote: View Post
Thank you for the feedback. There is still much to figure out.

For instance, these differences were observed by simply switching selection of input, not by removing any path that could be a noise path. The?noisy HDMI path was still there, just not selected.

Some careful diagnosis is certainly in order.

I want to be able to play 5.1 from the music server also. So I need to quiet the HDMI path.
Understood.
I am curious if you had changed out the hdmi cable you are using with another one just as a test. There are indeed noisy cables by way of the connectors on the ends amongst other things. Also can you try other hdmi inputs on your AVR ? Believe it or not I have one set of rca inputs on my Denon that have some issue in that they are not quite as clean as the others. I have to not use those inputs and yes I should have it fixed but the last time I sent it in it took 8 weeks to get it back so I just use another of the plentiful inputs.

I am also thinking that multi channel can be passed into the AVR via coax of toslink if the system is set up that way, are you able to do that ? Of course these options cannot pass video but it sounds like you wish to pass audio only.
It seems that sometimes electronics just do not always talk well to one another depending on how they are hooked together in a system. I was using two subwoofers once and had only one subwoofer out jack on the back of the Pioneer receiver. So thought I, I can just put a "Y" connector on the back of the AVR and voila, I can now send a signal to two subwoofers equally. Nope did not work. Somehow the signals got tossed back and forth, not sure why or how, and the sound of the entire system got skewed to the point wherein one channel was about 15db lower than the other. This is a funny hobby.

It is good you are experimenting with these issues in the best way possible, the free way for now before swapping out other components.

Good Listening

Jack

"For those who believe no proof is needed for those who don't believe no proof is possible"
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post #6 of 59 Old 12-11-15, 06:14 PM
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Re: Is Your System's Noise Floor Low Enough?

I really do appreciate all your efforts on our hobby, all the littel details you find that help us to make our systems preform to their fullest. Thanks Wayne!
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post #7 of 59 Old 12-12-15, 12:02 PM
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Good opening of the thread, you have already done a lot and your process is described well. What are the audio output settings for the various source machines?
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post #8 of 59 Old 12-12-15, 11:25 PM
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Re: Is Your System's Noise Floor Low Enough?

i have some noise/buzz... nothing playing amp on and preamp on... its making noise. I been lazy and haven't messed with it but need to work on it.

part of the issue is I can't have my amp grounded or it really does the ground loop buzz so I had to disconnect it. What I'm gonna have to try out is the rca->xlr bypassing the ground to see if that eliminates the cross talk.

It sucks too because I spent alot of time and energy running 10 dedicated circuits and ran all isolated grounds and have a dedicated ground bus in the panel that is isolated and a 2/0 cable runs down outside to 3 ground rods spaced in a triangle format 10' spacing.

I need to not be lazy and fix it. I'm also going to add some balanced transformers to the system.

Master Electrician

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post #9 of 59 Old 12-13-15, 01:35 PM
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Re: Is Your System's Noise Floor Low Enough?

well worked on my system and ended sleeving the bare ground cables in my outlet box to further isolate the cables... I did find the buzz culprit and it was my Krell not having the xlr shorting pins not installed. I made some out of some 10g solid wire and that significantly lowered the buzz/hiss I was experiencing.

I also moved my center channel off the stand it was on and moved my rack to absolute center and put my center channel on top the rack. By doing this I had to move the amp to the left side and the XMC to the right side and so I took alot of time isolating all the wires and keeping as much space as I could between them. I also reconnected the ground wire to the amp circuit and I'm happy to report that my system is "essentially silent" With all the equipment on with nothing playing and/or the music on pause and the volume at near silent, -20 and at 0 and also +12 I am experience nothing audible at the LP and nothing audible 6" away from the speakers. I do hear a slight... very faint hiss from the tweeter when my ear comes to within 1" of the tweeter.

This is a significant change from my previous and since I moved some things around I need to re-run Dirac and do some listening. I'll report back what I find.

Master Electrician

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post #10 of 59 Old 12-13-15, 01:39 PM Thread Starter
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That was a lot of work. We will be very interested in hearing what you discover in your listening tests. Good diagnostic work by the way. Those things are not always easy to find.


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