Originally Posted by ipeleshok
I've been having some issues with my new TX-NR646 receiver when playing 5.1 surround sound sources. I first noticed this issue during a 5.1 movie on Netflix, where I could hear a low decibel crackling static sound. The static is erratic, and the loudness is not consistent and can fluctuate, but what is consistent is that the static only appears during 5.1 sources. I can tolerate it for the most part, but it's fairly obvious during scenes of silence or low background noise.
Stereo sources are crystal clear on all speakers with no background noise, but 5.1 sources always initiate it. It's worth noting that stereo sources play comfortably at a volume of 30, but 5.1 sources require me to bump up the volume to 40-50. Also, the noise appears to only be coming out of the tweeters, but I'm not 100% sure.
My firmware is up-to-date on the receiver. I've tried Netflix on several sources, but Blu-ray sources do the same thing. I've also tried disabling DD+ as some forums have suggested, but to no avail.
Any advice? Any suggestions for further testing? Any settings I could adjust?
I would like to try another brand of receiver to see if there is similar behavior.
Originally Posted by ipeleshok
After some additional troubleshooting, I noticed that the static sound (digital noise) occurred only for HDMI input selections and even occurred when there was no HDMI source plugged in. This led me to believe it was a receiver issue, as I originally suspected. I exchanged the receiver for another one and, sure enough, the problem was gone. I'm assuming this was a faulty HDMI board issue, which are prone to Onkyo receivers.
I wonder if this is the same problem I'm having. I'm more hopeful since I read ipeleshok's post that he exchanged it for another one and the problem was gone, so I'll do that tonight.
It seems to me that the TX-NR646 introduces extra noise when the source is a 5.1 or higher signal. This can be DD+, TrueHD, any DTS variant or even PCM 5.1 like the AppleTV 4 outputs when it's set to auto (don't even get me started on that). Surely if the audio in the scene is loud and has a lot of background noise, you barely hear it, but if it's a low volume scene, like for example two people talking without background music, you can definitely hear a constant hiss. Here's the catch: initially I thought it might have been part of the movie's original audio, because when I paused them the hiss/noise was gone. But then I realized that it's because of the design of each device. My devices are a Sony BDP-S3100 Blu-ray player, a Roku 2 (4210X) and an Apple TV 4. When you're watching something on the Apple TV or on the Blu-ray player, and you pause it, they stop sending the bitstream to the receiver. If you press the bottom right button on the remote that shows you the information for the incoming audio signal, you don't see anything.
The Roku, however, behaves differently. When you're playing a DD+ title from Netflix or Amazon Prime, and you pause it, it keeps sending a DD+ signal to the receiver, which again you can verify by pressing the info button and it shows you that it's receiving said signal. Well, when I pause something in the Roku, I can tell right away that the hiss/noise is not in the movie or TV show, it's being produced by the TX-NR646, but only when the source is a 5.1 or higher signal. Obviously I notice this noise much more when wearing headphones because they are right next to my ears. However, if I use my speakers, that hiss comes out of all the speakers and the subwoofer, although of course in the subwoofer's case it's a hum rather than a hiss.
Last weekend I was watching "The Martian", which has DTS-HD Master Audio 7.1, and I didn't notice it too much until the end when Matt Damon is talking to a group of students. There's barely any background noise, but the hiss produced by the receiver was so loud that it was distracting. The interesting thing is that the Blu-ray player, when I pause it, pauses the movie immediately, but it keeps sending the DTS-HD Master Audio 7.1 signal to the receiver for about half a second, during which this noise/hiss is present, but no audio from the movie is, so you can tell it's definitely a problem with the receiver.
Obviously every receiver will introduce some degree of background noise, but my last one, a Pioneer VSX-1020-K, you had to raise the volume all the way up to hear any background noise coming out of the speakers or the headphones.
Another interesting fact; when I switch the source to PCM 2.0, in other words, plain old stereo, this noise is never present. If I switch the Roku to 2.0 and I watch anything and I pause it, I can't hear this hiss at all at normal volume levels. So this is a problem that the TX-NR646 has when processing multichannel signals. Somehow, when it has to convert those signals from pure digital to analog so it can be output through the speakers or headphones, it introduces a lot of noise.
I just hope that this is a matter of a defective unit rather than a design issue, because other than that, I'm very satisfied with this receiver. The sound is unbelievable for both movies and music, which is more than you can say nowadays for most receivers.