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DSP Xover project (part 2)
DSP Xover project (part 2)
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Old 13th January 2021, 09:39 AM   #3501
piecor is offline piecor  Italy
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@noviygera: see my (off-topic?) answer below.

The following may be of interest for other mates. I try to explain why I'd want to get the most from the analog input of the Najda.

Story
For a long time I thought that analog was superior and never experimented with DSP which requires ADC. Superiority of analog was derived based on the fact that none of the digital setting I tried reproduced certain album as the LP version. But later I discovered I was wrong.

I changed my mind when I started to record some of my rare LPs for friends using a basic audio card. Although I used a basic audio card the recorded digital version was quite close to the original analog. I started to investigate further like changing something in the analog chain... and every time the differences heard on the analog where pretty much kept in the digital data. One day I had a studio quality Weiss ADC borrowed from a friend working in the audio-video professional field. What a discovery! My digital copies were 99.99% sounding as the original LP. For certain albums I have several analog pressings and various digital masterings. In my experiments if the analog XYZ version sounded superior, the digital recording of XYZ still sounded better than any other digital master I had. This was confirmed in blind tests submitted to a number of audiophile friends.

Personal conclusions
I arrived to the conclusion that, when properly done, the ADC does not introduce any caveat. So, why one claims that the LP sounds better? Is it all about nostalgia, and desire to look cool putting 12" plastic disks on an ancient rotating plate? The answer I gave to myself is
  1. some of the music I love was recorded/mixed/mastered when the main hifi medium was the LP. And in those days everything in the recording/production was optimized for LPs. Only digital remasters done right can sound as good as the original LP version.
  2. Although with just 16bit the digital has theoretically 20dB of dynamic above the typical LP, starting from the early '90s the bad habit of applying huge amount of dynamic compression to make records sounding 'hot' took over. Therefore many digital masters and re-master are just crap.
  3. Music industry has become too fast. They don't take their time, everything is done too quickly today. A number of digital remasters are just crap. On the other hand, there exist small labels that do wonderful digital stuff, but their catalogues are limited
That's way in 2021, with powerful quantum computers, hi-rez, SACD, amazing DSP algorithms... I am in the quest for a proper way to have an advanced DSP machine fed with the prehistoric signal coming from a turntable! I can't believe that, but that is.

End
What I dream is a machine like the Najda with an in-built state-of-the-art ADC section!



@noviygera:
I have two arms, one with a MM the other one with an MC pickup. I use both and I select them based on the type of record.

For the MM I use an upgraded Counterpoint 3.1 preamp with top quality nos tubes. The Counterpoint needs to see a pretty high input impedance but when placed in the right chain it's real magic with certain masterings of the '60s-'80s (I'd go deeper into this but it's too off-topic).

For the MC I have a RJM audio phono clone preamp with extremely selected parts, there is a thread on this forum started here

The Phonoclone and VSPS PCB Help Desk

My unit has been stitched specifically on the ever green Denon DL 103 for which I have a sort of obsession! Nothing I tried with the DL103 sounds better to me (I also had very expensive SUTs). The Phonoclone needs to see at least 10K impedance, but something bigger than 25K is the way to go based on my experiments.

Over the years I had all sorts of top phono preamps (Audio Research, Audible Illusion, Convergent, Burmester, Threshold, and many others). But that's the best I had until now

Last edited by piecor; 13th January 2021 at 09:48 AM.
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Old 13th January 2021, 09:42 AM   #3502
shining31 is offline shining31  France
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Ahhhh LP voudou
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Old 13th January 2021, 09:58 AM   #3503
fluid is online now fluid  Australia
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Quote:
Originally Posted by piecor View Post
I am in the quest for a proper way to have an advanced DSP machine fed with the prehistoric signal coming from a turntable! I can't believe that, but that is.

End
What I dream is a machine like the Najda with an in-built state-of-the-art ADC section!
To me it makes much more sense to digitize the LP's you have and play them back from a computer where the wonders of volume leveling etc. can be performed

Each could be set up to be encoded at the best gain setting to get the best SNR and dynamic range in the digital copy, only needs to be done properly once.

When you try and do ADC on the fly you can end up having to tweak the input gain all the time or live with it being too low on everything. The analogue input on the Najda is not great. Any number of reasonably priced computer based interfaces would do a better job.
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Old 13th January 2021, 10:10 AM   #3504
piecor is offline piecor  Italy
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Quote:
Originally Posted by fluid View Post
To me it makes much more sense to digitize the LP's you have and play them back from a computer where the wonders of volume leveling etc. can be performed
[...]
this is time consuming for those who have collections of thousands of LPs like me.

And it is even more complicated, because we are all giant kids playing around with our toys, so If change a tube in the phono and I like it more... I have to re-record to see what happens. Doesn't work for me.

Regarding the input level, I don't see this as a problem provided that the analog level is adjustable. Currently I set the Najda input analog sensitivity to 2Vrms and I just tweak the preamp volume knob to not overload the analog input. For most records I don't have to move the volume knob too much, just few degrees up and down.

So, currently I think that If I want to keep the immense flexibility of a machine like the Najda, probably the only sensible thing for the analog input is to invest in a good ADC. But again, most of the good ADCs are thought for professional use. Not sure what to buy... well, the Weiss was wonderful but very expensive and still requires an input buffer which is not easy to set.

The input of the ADC is a critical piece not very easy to design. Nick explained this when I proposed to pay him for a custom analog input having a specific input impedance. I don't know what's the issue, but I notice that most ADC have very low input impedance (see Weiss for example). For pro this seems not to be a problem.

Last edited by piecor; 13th January 2021 at 10:19 AM.
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Old 13th January 2021, 10:19 AM   #3505
vinylnvalves is offline vinylnvalves  United Kingdom
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I think we are at the same point regarding the ADC, you have one advantage over me, my Nadja only has 1V rms input on the ADC. I am currently using the Project RS phonostage stage as the output impedance matches better than my Valve phono stage (Art 1 - derivative). The only “better” ADC’s I see for HIFI are the HRT line streamer (cheap), or the Brooklyn from M Tech.
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Old 13th January 2021, 10:29 AM   #3506
fluid is online now fluid  Australia
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Quote:
Originally Posted by piecor View Post
So, currently I think that If I want to keep the immense flexibility of a machine like the Najda, probably the only sensible thing for the analog input is to invest in a good ADC. But again, most of the good ADCs are thought for professional use. Not sure what to buy... well, the Weiss was wonderful but very expensive and still requires an input buffer which is not easy to set.
You like messing around much more than I have the patience for
Maybe try something like this into the i2s input of the Najda.

http://www.dimdim.gr/tag/adc/
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Old 13th January 2021, 10:41 AM   #3507
piecor is offline piecor  Italy
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Quote:
Originally Posted by fluid View Post
You like messing around much more than I have the patience for
Maybe try something like this into the i2s input of the Najda.

http://www.dimdim.gr/tag/adc/

tnx I'll look at it, but I see last lines mentioning that an input stage is needed!
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Old 13th January 2021, 04:32 PM   #3508
30m20 is offline 30m20  Europe
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Default Why should post-gain not be positive?

Hi all,
even though Nick´s NUC-Manual is really great and I admire his very understandable writing, there is one question I have since the beginning:


On page 9 he writes, that generally, a positive post-gain "is the clue of an improper gain structure."
Like certainly others, I found out, that a 48 dB-filter at say 5KHz needs a pre-gain of -8 or -9 dB to avoid clipping. Why not push a bit upwards again with a positive post-gain (to avoid to have to attenuate the other channels to the same lower level -> lose resolution)?
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Old 13th January 2021, 04:58 PM   #3509
30m20 is offline 30m20  Europe
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@vinylnvalves: Yes, I wanted to test balance via digital input, but my measuring system has only an analog out. Just found old test-CDs and will do that...


Nice to read that analog in "quality" might be caused by impedance mismatch. That would be an explanation . . . But how to compensate?
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Old 13th January 2021, 05:57 PM   #3510
vinylnvalves is offline vinylnvalves  United Kingdom
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What’s a CD ... CD player went about 10 years ago.. all streamed music nowadays. I will download a test signal.
Impedance mismatching is the same as for any driving load. Understanding Impedance
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