Software Converting HDCD

I'm finally converting the HDCD albums on my harddrive to 24-bit, using ffmpeg.

I should have done this years ago.  

Instead I depended either on playing the physical discs themselves in my Denon DVD-9000 player (and resampling back to digital for my crossovers and EQ's), or running the SPDIF single into the DVD-9000 from my computer through Sonos.

I spent many hours carefully setting up a HDCD-resampling path to my system.  Every time I changed the system, I had to move things around to keep it still working.  I was doing more of that setup stuff than actually playing HDCD's it seemed.

But there really wasn't any reason not to use a software converter, either foobar2000 or ffmpeg.

A few years ago I installed ffmpeg on my computer mainly so I could just TEST what kind of HDCD features discs had.  I didn't pay attention to the fact that the script was actually doing full conversions of HDCD files so it could make reports about them, and then just trashing the conversions.

Here's the simple script hdcd-convert that will convert all the files that are wildcard specified:

#!/bin/bash

rm junk.flac 2>/dev/null

for name in "$@"

do

    ffmpeg -i "$name" -af hdcd "$name".hdcd.flac

done

I run this script in a terminal with a command like this:

hdcd-convert *.aif

This does both the peak extension and the gain adjustment.  AFAIK nobody does the variable filters in playback, and I'm finally coming to believe that (though I still have a bunch of test resamples of my favorite HDCD discs played on the best HDCD player I have...the Denon DVD-9000).

Checking the actual Denon 9000 manual, no mention is made of Museatex (as I previously reported incorrectly) nor their patent on switched playback filters, which btw is:

5,388,221

The Denon manual does list a bunch of patents used for HDCD, but not that one.  In fact the listed patents for HDCD all have higher numbers than that one too.

5,479,168

5,683,074 

5,640,161 

5,808,574 

5,838,274 

5,854,600 

5,864,311 

5,872,531

The Denon DVD-9000 provides no way to turn HDCD decoding off, so I cant test both ways through the same device.

The peak extension is a VERY BIG DEAL on the discs that have it, which include Mephisto & Co., one of my all time favorites, and most other Reference Recordings CD's (though strangely about half of mine either don't have HDCD or don't use it except for flipping the useless Transient Filter flag).

I'm searching through my other discs for those that use HDCD.  Neil Young, Grateful Dead, and many others used it.

I'm pretty much in line with Charlie Hansen's thinking about HDCD.  It had some good aspects and some scam aspects.  I do not consider it entirely a scam.  In many ways it makes sense, and it could have been a solution to the "loudness wars" (where newbies use the effectively compressed undecoded discs, and Audiophiles get the fuller dynamic range).  But for various reasons, we got the unabated loudness wars instead.

Charlie dismisses the potential usefulness of the transient filter flag (TF) in a weird way.  He says that when the sampler uses a filter with higher leakage of aliases, it makes no sense that the playback decoder would also use a filter with higher leakage of aliases.

Funny because Charlie had his own digital filter design that had very nice impulses but far more alias leakage then the usual digital filters.  He should have known why someone would do that: for better transients!

Actually, in my mind it makes no sense to do what Charlie did, use a "transient correct" but high leakage filter All The Time.  That would contribute grunge to dense passages.  The variable filter option sounds like it might be a better idea than his to me.  The TF should only be used for simple transients, not thick textures.

Arnie Kruger however had a very simple but (mostly) devastating critique of HDCD:

The core problem is that the higher bit depth is not realized in the actual signal, not even in the master recording.

It is easy to make 24 bit recordings where the bottom 9 or more bits are noise. As a matter of fact, that's always what happens when you make real world recordings.

At playback time it doesn't matter whether the bottom 9 or more bits as represented in the analog domain were noise sourced in the original recording environment, or whether they were sourced in the dither of a 16 bit medium. Its all noise, not music.

In this same thread Arnie puts HDCD in the same category as "true high resolution" formats like DVD-Audio, SACD, though it only provides about a bit or so of effectively increased resolution.

(There's no actual increase in resolution at all, except that it's shifted over a slightly wider range, making it "effectively" increased where it's more needed.)

But Arnie simply believes none of that is necessary.

While I completely agree that electronic noise in the recording studio is just as bad as electronic noise in the playback system, acoustic "noise" in my opinion isn't really noise at all...it's part of the product...the ambience.

Early indications are that the noise level from my Denon DVD-9000 transcriptions is around 92dB or so without any kind of weighting.  With proper A Weighting that might improve to around 105dB or so I think, but I'm wondering why I'm not getting closer to the spec for my DA-3000 sampler which is 114dB or the Denon DVD-9000 spec of 118dB.

But I argue now and still that "noise" and "lack of resolution" are not the same thing.

I still believe it's important to capture the "resolution" even if a tad bit of noise is being added.

So that's my second disagreement with Arnie.  Though I feel a bit less strongly about it (the difference between noise and lack of resolution might not be very big in many cases).

Anyway, with my transcription system having unweighted noise around -92dB, when I amplify it way up (by 90dB) I can see when the actual noise from the recording starts a fraction of a second before the music itself.  The "noise" (which includes ambience of course) is easily much higher than -92dB on the recordings I've looked at.

The hardware conversions I'm doing using the Denon 9000 will always have more noise than the software conversions.  There probably isn't a real reason to do the hardware conversions, but I'm doing them to satisfy myself that they aren't necessary.