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The amazing <img  realtek phono preamp?
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Old 7th July 2020, 12:55 AM   #51
grufti is offline grufti  United States
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The amazing <img  realtek phono preamp?
De-click from LP typically works better before RIAA. Can you route your audio that way for realtime play?
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Old 7th July 2020, 06:58 AM   #52
ariendj is offline ariendj  Germany
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Declicking before RIAA is something that I have been meaning to do. Rerouting the signal is no problem as it is all software. I'll try this out in the next few days.
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Old 8th July 2020, 10:06 PM   #53
ariendj is offline ariendj  Germany
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Originally Posted by grufti View Post
De-click from LP typically works better before RIAA. Can you route your audio that way for realtime play?
I did not get around to rerouting my setup yet. Still on my to do list.

I felt like listening to some classical music today and tried the declicker with that. The results are excellent. The few clicks that are still left are attenuated and the whole experience is a lot more pleasant. First round was the Berlin Philharmonic Orchestra playing Beethoven's 5th conducted by Karajan. I know this record really well and was surprised at how clean the resulting audio was. As there are no drum beats in Beethoven I could not hear any problems caused by the declick. The result was very good.

The next record I tried was the Chicago Symphony Orchestra playing Scheherazade coducted by Fritz Reiner. I think it's a lovely piece of music but it has such a large dynamic range that ticks and pops make it unlistenable to me for the most part. Once again the declick works like a charm and I can actually concentrate on the music instead of being annoyed by the medium's defects.

Going back to a Steely Dan record (that needs no declicking) the problems with the algo were obvious again: The transients on the drums, especially the snare, were attenuated. It sounds somewhat similar to a worn out cassette tape as far as impulses are concerned. You could call it a little washed out. Still very listenable but not fully transparent.

I went back to the file with the residual noise that the filter removed from my Rickie Lee Jones needle drop. Looking closely at the 'false positive' clicks I noticed that they were exactly on the beat of the music.

After some googling the program called aubio came up. Among a lot of other things it does It can take a piece of audio and print out the timecode of every beat. I can even tell it to look specifically at the onset energy

This command ...

Code:
aubiotrack -O energy -i rickieleejones.wav
... will do the trick and the timestamps that this command prints out line up perfectly with the false-positive clicks.

Now I need to figure out a way to have the declicker mute itself a few samples around the timestamps that the aubiotrack command detects as the beat. This way the amount of false-positive samples could be greatly reduced on any music with drums.
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Old 13th July 2020, 10:35 PM   #54
ariendj is offline ariendj  Germany
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I went back to the file with the residual noise that the filter removed from my Rickie Lee Jones needle drop. Looking closely at the 'false positive' clicks I noticed that they were exactly on the beat of the music.
Two wrongs don't make a right. Aubio didn't really help me in separating drum beats from clicks in the audio. I had to do a lot of tuning to get it to detect the beat right and then the drum hits were still off by a little bit. If it was really that easy someone else would have done it before me, I guess.

Another weird idea I tried out was using 'spleeter'. It's a fun piece of software that will split an audio track up into multiple tracks, like vocals, bass, drums and "other". I hoped that this could maybe differentiate between clicks and drums so I'd be able to use declick on anything except the drums and then add the untouched drum track back in. Alas, just as any other software so far it lumps the clicks in with the drums. No real benefit here, unfortunately. But it still is impressive to see what ML can do nowadays.

Spleeter uses tensorflow, a machine learning program and can be trained to split anything that it has been fed separate tracks of. So in theory I could train it with music on the one hand and vinyl noise on the other and then teach it to separate the two from any audio I feed it. I don't think that I'd ever have the time to seriously attempt this though.

I'll just try to declick before RIAA next, it's probably still the only thing that can improve the results I am getting with music containing drums. For anything without drums I must say that the FFmpeg filter is very pleasant to listen to even on quieter records. In that case the resulting audio sounds flawless to me.

On the ceramic cart front I have not made any worthwhile progress. I tried to mount the Philips GP 215 on a Philips AF 777 thinking they might be compatible but the GP 215's half inch adapter does not fit at all. I'll have to try the GP 215 with my Grundig PS 4500 next. As far as the GP 390 is concerned I'll probably mount that to the AF 777 as is almost the same shape as the factory installed GP 400. I still have to mount the new stylus on the 390 though.
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Old Yesterday, 09:50 PM   #55
ariendj is offline ariendj  Germany
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Quote:
Originally Posted by ariendj View Post
Attachment 852226

As all the graphs were done with simple peak hold, both graphs show absolute worst case behaviour. Of course K2 looks insanely high but I don't think this aspect has any practical relevance. What I do find interesting is the 80dB difference between the +18dB peak and the noise floor at that same frequency. More than I expected, for sure.
What the graphs I mentioned also show is that with low frequencies the groove noise is barely a few dB louder than the LF noise generated by the amplification in the Realtek chip.

During regular listening this was not as obvious as it was when listening to some needle drops with my IEMs. With the IEMs it was clear that on some records the groove noise was louder and on others the low frequency hiss from the gain stage was louder.

While I'm trying to stay as close to the original premise of this thread, that of the $0 preamp, it is not $0 anymore. I bought a 30dB preamp module meant for microphones, the Kemo Electronic M237. It costs about $/ 12 and claims a bandwidth of 8Hz-60kHz and distortion below 0.02%.

So the project is no longer "free" but "cheap" and on the hardware side no longer "no effort" but "low effort". I'm trying to find a balance between doing as little as possible and as much as needed.

I connected the module to an old SMPS that was left over from an external hard drive. Connected some very short RCA cables and started my software RIAA EQ. Now groove noise is clearly louder than any noise from the preamp stage except for the fact that my test setup is picking up some mains hum from somewhere. Considering that I did not put any effort into shielding for this first test this comes as no surprise.

Input impedance for the module is specified as 100k so I'll add a 65k load for the 100pf cable capacitance I have as Bill suggested in the "what about digital RIAA" thread. Shielding must be taken care of and then I'll get out the test LPs to EQ this setup to be as flat as possible. I'll re-evaluate my crosstalk cancelling setup but I don't expect the values to change as crosstalk will be determined by my cartridge alone.

My long term goal is to (learn how to) build a small preamp stage with some NE5534s. Until now my attempts have not been all that successful as my boards would make popping noises and oscillate. Recently I learned about decoupling caps and I think the oscillation was because I never bothered to bandwidth limit the feedback loop on the opamps. I'm doing my best to take this one step at a time. Patience is something that I'm still learning
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