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TOPIC: nanoAVR HD Distortion

nanoAVR HD Distortion 7 months 3 weeks ago #41883

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So, I FINALLY got back to working on my theatre system, and was ready to configure a nanoAVR HD ahead of a nanoAVR DL.

I started with just the nanoAVR HD for bass management, and I find, that the damn thing distorts! I am running it bypassing everything, and it still distorts. I took it out of the loop and verified the distortion is gone.

What gives?

I am running v 1.30 firmware, and tried reinstalling it to no avail. This is a real bummer.

I have verified that I am feeding it 1080p 60Hz 4:4:4 video with 7.1 48 kHz LPCM audio (from the secondary HDMI "audio" port of an Oppo BDB-103D (which does not do HDCP)).


Anyone have any ideas?

On edit: Hmm. I noticed the nanoAVR HD outputs at 96 kHz sample rate. While this is fine to feed a nanoAVR DL which will output at 48 kHz it may be out of the range of my downstream equipment. I will try configuring it as it is, and then see if the distortion goes away when it feeds a nanoAVR DL.
Last Edit: 7 months 3 weeks ago by rhollan. Reason: possible idea
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nanoAVR HD Distortion 7 months 2 weeks ago #41903

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Yeah: seeing the noise on all channels. Dunno if it is because I am.i. the calibration app or if my DACs are noisy.
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nanoAVR HD Distortion 7 months 2 weeks ago #41905

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To be clear: distortion is gone now that the nanoAVR HD feeds the nanoAVR DL. But I now have a noise issue: my noice floor is way too high.

Specifically, I have the following chain: HDMI out of an Oppo 103D to a nanoAVR HD to a nanoAVR DL to an hdtvsupply (www.hdtvsupply.com/hdmi-to-hd-sdi-converter.html) hdmi to SDI converter to a Blackmagic SDI to AES audio converter (www.blackmagicdesign.com/products/minico.../techspecs/W-CONM-22) on to two AJA AES to analog audio converters (www.aja.com/products/ada4).

I know I could get analog audio out of the Blackmagic SDI to AES audio converter (it is switchable), but only 4 channels so I opted for using it to produce digital output and convert with two AJA ADA4s.

The problem is that the noise floor out of the ADA4s is way to high. This surprised me as AJA has a reputation for good products. So. It's either coming from there (I can try the Blackmagic SDI to audio converter in analog output mode), or the Blackmagic converter (in the digital domain? I doubt it: bits in equals bits out), or the nanoAVRs in their processing.

I am open to suggestions. If it turns out the be the ADA4s and the Blackmagic SDI to audio converter is better, then I will pick up another one and use one for channels 1-4 (front left, center, right, sub) and the other for 5-8 (left and right surround and left and right rear). But I would be surprised if the Blackmagic converter is better than the AJA ADA4. (Blackmagic converters have a reputation for cheapness, which is why I chose the AJA converters for the analog conversion).

If it turns out to be the nanoAVRs in the digitial realm, well, I am dead in the water as far as miniDSP is concerned. Given how many satisfied customers there are I am hoping this is not the case.
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nanoAVR HD Distortion 7 months 2 weeks ago #41967

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It may be that I need to address the signal level to the amps better. For a rough tune up I left the master volume in the Dirac Live Calibration tool at -48 dbFS, started with the channel sliders at full, and tuned the amp attenuators (these are professional amps, Crown XLS 1002 and 1502) with attenuator controls) to get an acceptable level at the mic (-12 dB). This was more than half way up the amp attenuators.

Ideally, one should send the strongest signal possible to the amps and attenuate it on input, to maximize SNR.

So, I will try tuning at -20 dbFS which should let me increase the amp attenuation (decrease the level) by 28 dB. That would also let me fine tune the amp attenuation settings as I am striving to reach peak THX reference levels of 105 dB (C-weighted, (0 dbFS), so 85 dB at the mic. If that proves too loud for the mic, I will drop it another 10 dB (THX reference levels of 85 dB with 20 dB headroom is *very* loud for extended periods).
Last Edit: 7 months 2 weeks ago by rhollan.
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