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Topic: SACD decoder setup (Read 3895 times) previous topic - next topic
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SACD decoder setup

Hiyas,

I am advised that I should increase output PCM volume to maximum for best result when making conversion of SACD to FLAC.
I wanted to make sure this adjustment is qualitywise safe mainly with regard to prevention of peaks clipping.

I was also curious if Saracon is still better algorithm for SACD conversions over foobar SACD decoder.

Thanks for input.

Re: SACD decoder setup

Reply #1 –
DSD's theoretical maximum level is 6dB higher than PCM's (one bit.)  By spec it should never get louder than about +3dB or +4dB and even then only rarely.  On the other hand there are some SACDs out there that go beyond that (the Michael Jackson "Thriller" SACD comes to mind.)

To preserve the full dynamic range you shouldn't raise the level of the PCM when converting, but then if you don't use something like replay gain, etc. your DSD derived material will be 6dB quieter than the PCM material, all other things being equal.

Still, some SACD players out there never provided the full DSD range anyway.

To convert DSD to PCM all you need to do is low pass filter the output: the filters in foo_input_sacd are fine implementations and allow you to select the output rate, choose some different implementations and some various low pass cutoff frequencies (depending on how your system handles the remaining ultrasonic energy) and, if you choose you can load your own filters...

I don't know the Saracon DSD to PCM conversion details, but, in principle, there's no reason they shouldn't work just fine too.

Re: SACD decoder setup

Reply #2 –
Thanks for the technical bg, so to be safe, instead increasing output volume I should always apply RG info?

Quote from: tedsmith on
To convert DSD to PCM all you need to do is low pass filter the output: the filters in foo_input_sacd are fine implementations and allow you to select the output rate
Would you generally recommend optimum lowpass filter or is the choice individual per release?

Re: SACD decoder setup

Reply #3 –
Replay gain using "apply gain and prevent clipping according to peak" provides the same effect as picking the maximum non-clipping value for the PCM level raise during DSD to PCM conversion (assuming you convert to 24 bits instead of 16 bits.)  "Apply gain" without using the prevent clipping will be similar to raising the PCM level to 6dB and using replay gain on that.  So, with replay gain, you can delay the choice of whether to clip or not to playing.

The optimum cutoff depends more on the capability of your system to deal with ultrasonic energy.  SACDs have a maximum level of ultrasonic noise of -40dB FS (1/100th FS) with a filter around 50kHz  The 30kHz filter default in foo_input_sacd is pretty conservative.  If your system is linear to above, say 50k or 80k you might want to experiment with using Saracon with a higher filter cutoff and listen to see if you hear a difference you care about.  Some systems will modulate the ultrasonic noise back into the audio band (either in your preamp, amp or in your speakers) and cause low level but audible noise - in that case 30kHz is probably the best bet.

The choice of 32bit/64bit and direct/multistage is mostly subjective.  I prefer direct simply because it only does one stage of filtering instead of multiple stages of filtering, but your ears may disagree with mine.  Similarly I would use 64bits just because processing is cheap these days and it should theoretically be more precise.

Re: SACD decoder setup

Reply #4 –
You can certainly raise the level (and it will not impact the audible dynamic range significantly) to a value less than the point where it overloads ('clips').  You can monitor this using the foobar Console while doing the conversion -- it will tell you when there is an 'over'.  I try first at +6dB and if necessary re-do in increments of -1dB until there are no overloads.  I convert to 88kHz/24bit PCM.

Typically some amount of level increase is possible.  Thriller is the rare case -- the only I've encountered -- where overload was mistakenly baked in to the SACD mastering, though only in a very few moments (on 'Beat It',  IIRC - and it isn't noticeable to me) .