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In Reply to: RE: Loudness - SACD versus CD posted by murali on July 10, 2015 at 05:28:12
Hi,
> The most and immediately noticeable aspect while playing a SACD
> disc for me is the extension of the soundstage from front to back
> and sides, like lifting a veil.
You get the same effect by lowering the volume instantly by 6dB, try it.
> However, I find that the loudness is reduced
Yes, DSD has a recommended maximum level that is 6dB below what traditional digital audio calls "0dBFS" (it is in the Purplebook Spec for SACD). This is in part down to fundamental limitations of the format, many Delta Sigma modulators with very high order modulators are not stable at high levels.
If you have a dedicated DSD DAC it is possible to re-scale 0dBDSD to give the common 2V output.
If you have a DAC that processes DSD and PCM in a single chip you need to include this gain scaling in the audio circuitry, switchable (kind of the opposite of what HDCD mandated when it was an active format)..
This tends to be non-trivial (it needs extra stages or complex switching).
I have solved this problem for an upcoming product, it will have identical output levels for 0dBFS (PCM) and 0dBDSD, interresting challenge.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Follow Ups:
This deals with the part that you can as a DAC designer, but it requires that the two files have to match "0 dB" in both formats. That's up to the mastering engineer.
As HDtracks discovered early on, if you take a DSD file and convert it to PCM such that a 1 kHz tone lines up on both formats, you may get clipping on the PCM file on some (many?) DSD recordings. To make things work properly it is necessary to make adjustments. You may be able to go the other way automatically if the PCM recording is made correctly (which means that the RMS power in the loud portions should be around -20 dBFS). However, due to the loudness wars, this is not what most PCM recordings look like. Many have intersample peaks that will get digitized in DSD and these can be several dB higher than the samples. On normal recordings with occasional crests this is unlikely, but on loudness war material this is quite likely, because in many cases the music has been turned into square waves. Some mastering engineers even go so far as to clip their analog to digital converters to get extra loudness. IMO, these people should be taken out back and shot. (Most will claim they are just trying to make enough money to keep their studio open and feed their family.)
I get pretty good matching with most material using HQPlayer. However, I have had to use -2 dB of digital gain reduction to avoid clipping with some material. This may not be just the intersample peak issue, because I am also doing some digital room correction. HQPlayer has a counter that indicates the number of samples that were over its limit.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Hi,
> This deals with the part that you can as a DAC designer, but
> it requires that the two files have to match "0 dB" in both
> formats.
That is a job for the Testtone generator in Weiss Saracon.
But it is not so simple.
Because SACD goes above "0dB" some masters go into this headroom. So you need to in effect scale 0dBDSD to equal 0dBFS to cure the loudness problem and after that you need to allow for an extra 6dB headroom over and above 0dBFS.
As long as you are running on USB or Battery power for smallish more or less portable devices this can get difficult, as you need > 4V RMS on a single ended connection and then the customer has some stupid Amp/Preamp with an electronic volume control that runs on +/-5V and hence once you give them the > 4V RMS it will clip their system.
One could of course attenuate PCM by 6dB, but then if customers compare your DAC to ones with standard levels many will claim the lower output DAC lacks dynamics and so on.
So, not so simple.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
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