SACD->PCM: strange high frequencies up to 88K, pls advise

dvdr · Joined: 11 May 2010 Posts: 2

Hi
I tried to digitize a SACD using the method to output PCM via HDMI, then feed it to an HDMI->SPDIF adapter and record it from there using professional hard-&software.
I was using a professional AD/DA: RME FireFace 800, that can accept SPDIF-signals up to 192k, and professional recording software Samplitude V8.
Analyzing the recorded signal, I do get very strange, constant frequencies up to 88k (with 176.4 sampling rate) and up to 44k (when limiting PS3's SPDIF-output to 88.2k). These frequencies are not content-dependent. No matter, what music / SACD I feed, they are there at constant levels, the are up to -40dB in the region of 80kHz! These "residues" are independet of Bit-Mapping options selected, as well..
Attached graphs do show this - any idea, how I can avoid that and what is happening there?

The spectrum analysis of the output at 88.2k sampling rate:

The spectrum analysis of the output at 176.4k sampling rate:

PS3SACD · Site Admin Joined: 17 Aug 2007 Posts: 316

The phenomenon you're witnessing with the out-of-band noise must be noise shaping, a technique used with delta-sigma modulation and DSD, hence on SACD.

See http://en.wikipedia.org/wiki/Noise_shaping

It continues to be a source of much debate.

dvdr · Joined: 11 May 2010 Posts: 2

Thanks for your answer!
I knew about noise shaping, but constant out of band frequencies of -30 // -40 dB below peak level of the main signal? Could that really be??? I am worried, that this might "cover up" harmonics or be sonically problematic otherwise....
I found a picture on the web, that show noise shaping, but seems to have completely different levels - is that somehow comparable to my situation?

The complete post is here:
http://pro-sacd.lefora.com/2009/08/30/impulse-response-analog-pcm-and-dsd/

PS3SACD · Site Admin Joined: 17 Aug 2007 Posts: 316

Not sure. Personally I'm interested in the science behind SACD but mainly care about how it sounds. I'm not intimately familiair with the details of noise shaping.

Bruce B · Joined: 01 Sep 2010 Posts: 1

This is DSD high frequency noise shaping. We see this on all the DSD files we get off of SACDs

Regards,