[LAD] Re: [linux-audio-dev] Direct Stream Digital / Pulse Density Modulation musing/questions

[Maitland Vaughan-Turner]

>
> ------------------------------
>
> Message: 2
> Date: Mon, 24 Sep 2007 11:28:17 +1000
> From: Erik de Castro Lopo <mle+la at mega-nerd.com>
>
>
> First off, why are you reprising a 4 year old thread if you don't have
> anything new to add?

Uhh, what about experience?  I've actually used a 1-bit recorder.  You
can talk about theory and quote papers all day, but that doesn't mean
*anything* compared to actually making recordings all day.

Also, things have changed a lot in 4 years.  Now 1-bit recording is
available to everyone.  Unfortunately, however, there are no linux
alternatives for dealing with 1-bit files.  I just thought a bit of
discussion on this list might help with that.

>
> Maitland Vaughan-Turner wrote:
>
> > So..?  Most PCM converters utilize a 1-bit stream also.  Why not
> > utilize all the tools available for the task at hand?
>
> Yes, but you need to analyze what you are doing or the next thing
> you know you are paying mega dollars for triple gold plated single
> direction, rare earth metal interconnect cables and other such
> snake oil.
>
> > As for processing, you can look at a PCM representation of a waveform
> > to ease the processing load and then just apply the changes to the
> > orignal DSD stream without ever having to process in the 1-bit domain
> > directly (which is way more processor intensive since you have to look
> > at a huge chunk of the stream in order to extract the amplitude data
> > that is available in each multi-bit sample).
>
> Problem : the conversion from DSD and PCM is lossy [0], hence doing
> DSD -> PCM -> DSD -> PCM is a bad idea.

that's true, it's not the route I would take, but doing some effects
in PCM and mixing those with the original stream (either analog or
pure DSD mixing) results in more clarity than working wholely in the
PCM domain.

>
> > IMHO, though, the hippest alternative at present is to process a DSD
> > stream in the analog domain and re-record it to DSD.
>
> Two problems:
>
>   - A-to-D converters are limited to about 20 bits of SNR due
>     to things like silicon junction noise and those noisy
>     electron thingys.

heh, i didn't say it wasn't lossy I just said it was hip.  Like, it
sounds cooler (to me) than using a DAW.

>
>   - All commonly used audio A-to-D converters are 1-bit so every
>     time you go to analogue and then into a digital effects box
>     you are doing another DSD to PCM conversion.

Is this a bad thing?  I never said PCM sucks or anything.  Haven't you
ever used an effects send/return, anyway?  You don't have to send the
entire signal through the box.  The affected signal is mixed with the
original signal.

I'm also using DSD to record a guitar running through a 20bit PCM
hybrid effects  and a 16 bit keyboard and occasionally a V-Drum set.
Oh the blasphemy!  :)

>
> See reference [0] below.
>
> >  This results in a very "analog" sound.
>
> So, you have a way of objectively measuring how "analog" something
> sounds? I'd be interested in hearing your methodology.

not objectively.  I just use my ears.  I record my band and the detail
and clarity of the recording in DSD format is striking (compared with
PCM).  This kind of detail I can only hear when playing vinyl records.
 That's why I say it sounds more "analog."

Intuitively, one could also say that more sample points yield a
waveform that is closer to a continuous, analog waveform.  Thus it
sounds more analog.

>
> >  These days you can get analog gear with a
> > respectable dynamic range for a song (Mackie Onyx anyone?).  When you
> > can get a 130 dB S/N ratio in the analog domain you really don't lose
> > too much converting back and forth from 1-bit domain.
>
> Where is you analogue to digital converter which also has 130dB SNR?

well, right, I'm saying the analog gear (that I have) is higher
quality than the digital gear.  Of course, there is going to be some
change in sound everytime you switch domains, but is it a loss or is
it a gain??  I think it mostly depends on the skills of the audio
engineer.

>
> Erik
>
> [0] Why 1-Bit Sigma-Delta Conversion is Unsuitable for High-Quality
>     Applications,
>     Stanley P. Lipshitz and John Vanderkooy
>     http://sjeng.org/ftp/SACD.pdf

Thanks for the link.  My whole point of digging up this old thread
though, was to say that I've tried it, and my ears tell me that the
papers are incorrect.

IMO, 1-bit recording is LSD not snake oil...


...have some of the kool-aid, it's the good stuff ;)


~Maitland