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Vinyl, pure analogue system - room eq, digital vs analogue?


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Having just set up a nice budget vinyl system in a separate room, and loving the new Black Diamond stylus on the AT95 I am using on the turntable (posted about this just recently), I started thinking about room/system eq.     To my ears, bass gets absorbed too much in this room, and I think there is a bit of a peak at a couple of kHz.  Haven't measured anything yet, just the way this  system(and my home theatre) sounds to me.

 

Now, after recent experiments with a raspberry pi running software as a phono eq, I could easily set one up to do the room eq as well as phono.  However, that puts an ADC and a DAC in the signal chain.   Alternatively I can add an analogue graphic equaliser into the chain.  I know of the shortcomings and opinions of that too.  But which is worse?  I am feeling like staying purely analogue.

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Try different positioning first to get better bass response. The simulator in REW does a decent job and will show you where the dips are. Then do a measurement in your room to see where the dips are. if you want it to be low budget best option is add a sub. I found really hard to beat room mode just by using EQ on the speaker. Without a sub you have to boost the under 120hz by a lot to beat the room mode. 

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4 minutes ago, mloutfie said:

Try different positioning first to get better bass response. The simulator in REW does a decent job and will show you where the dips are. Then do a measurement in your room to see where the dips are. if you want it to be low budget best option is add a sub. I found really hard to beat room mode just by using EQ on the speaker. Without a sub you have to boost the under 120hz by a lot to beat the room mode. 

 

For sure, but I think separately about nodes and room eq.  I have adjusted position and angle of the speakers so nodes don't upset me where I sit to listen, but still after that, there is the general room eq to deal with.  The peak I mentioned may be the speakers, and it turns out to be at about 7 kHz, and 3 db or so attenuation tames it nicely.  The slight bass deficiency is dealt with as you say, but raising the lower frequencies, ramping up to about 6db at 50 Hz and under.

 

Currently using the despised analogue graphic eq method.    I wish I had a handle on what mangles the signal more, the graphic eq or the ADC/digital filter/DAC sequence.

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1 minute ago, aussievintage said:

The slight bass deficiency is dealt with as you say, but raising the lower frequencies, ramping up to about 6db at 50 Hz and under.

in my experience most room mode dip is more like 20db. and if you have a relatively full range speaker 50hz dip will have a peak before it around 30-40hz. so you want to just target that 50hz dip and boost it by a lot but don't touch 30-40hz. But definitely o a freq sweep in your room first to know exactly where to tweak. I use minidsp and it does a good job but I won't use it to eq a speaker especially a good speaker for a sub it does an ok job. 

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5 minutes ago, mloutfie said:

in my experience most room mode dip  is more like 20db. 

 

That's why I say it isn't due to a room node.  I think it's simply absorption by the carpet and furnishings.  6db  is plenty to bring the frequency response back into balance.  20db would be WAY too much.

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if you feel the 6db is enough I guess that is good but if you want to skip eq I see might still a good idea to do a freq sweep while moving the speaker around again cos carpet and furnishing doesn't tend to normally absorb much under 120hz

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1 hour ago, aussievintage said:

I wish I had a handle on what mangles the signal more, the graphic eq or the ADC/digital filter/DAC sequence.


Purists will probably disagree with me, but I reckon AD/DA conversion will be completely transparent. 
Doing EQ digitally is far better than via an analog graphic equaliser 

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1 hour ago, aussievintage said:

 

That's why I say it isn't due to a room node.  I think it's simply absorption by the carpet and furnishings.  6db  is plenty to bring the frequency response back into balance.  20db would be WAY too much.

 

Carpet won't absorb bass frequencies and furnishings will do little to nothing especially at lower bass frequencies.

Really, you can never absorb too much bass because ideally the bass outputted from your speakers should just go by your ears and never be reflected back from your room.

Edited by Satanica
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32 minutes ago, sir sanders zingmore said:


Purists will probably disagree with me, but I reckon AD/DA conversion will be completely transparent. 
Doing EQ digitally is far better than via an analog graphic equaliser 

 

OK, so if we accept adc/dac transitions are transparent,   is the convolution fir filter - or even a software graphic equaliser,  transparent, or do those digital mathematical manipulations also cause problems just like the analogue filters?

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32 minutes ago, Satanica said:

 

Carpet won't absorb bass frequencies and furnishings will do little to nothing especially at lower bass frequencies.

Really, you can never absorb too much bass because ideally the bass outputted from your speakers should just go by your ears and never be reflected back from your room.

 

 

Fair enough, then it's just the speaker frequency response probably, that I am correcting for.   

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1 hour ago, aussievintage said:

 

OK, so if we accept adc/dac transitions are transparent,   is the convolution fir filter - or even a software graphic equaliser,  transparent, or do those digital mathematical manipulations also cause problems just like the analogue filters?

 

I'm stretching my knowledge here but as far as a recall, the benefit of digital filters is that they can correct frequency without messing up phase (and indeed they can also correct phase). As far as I'm aware, analogue filters are unable to change frequency response without messing up phase response.

Plus you are putting a whole bunch of extra physical components in the signal chain which may add noise etc

 

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18 minutes ago, audiofeline said:

I would tend towards seeing if there are treatments you can do to the room before playing with the electronics.  eg. reflectors, sound absorbers, bass traps, etc. 

 

 

 

Ah, yes, but it is also a common living space, so I will be restricted on what I can do.  No matter, it is only a secondary area for music, my main systems are in a completely different part of the house.

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2 hours ago, sir sanders zingmore said:

 

I'm stretching my knowledge here but as far as a recall, the benefit of digital filters is that they can correct frequency without messing up phase (and indeed they can also correct phase). As far as I'm aware, analogue filters are unable to change frequency response without messing up phase response.

 

 

 

Thanks.  I hope you are right.

 

2 hours ago, sir sanders zingmore said:

Plus you are putting a whole bunch of extra physical components in the signal chain which may add noise etc

 

As you are with ADCs and DACs.  Lots of analogue circuitry, amplifiers along with the digital, plus the digital noise leaking into those same amplifiers from the high-frequency digital circuits and computers housed in the same box.    That's part of the reason for preferring a true pure analogue system.    

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1 minute ago, aussievintage said:

 

Thanks.  I hope you are right.

 

 

As you are with ADCs and DACs.  Lots of analogue circuitry, amplifiers along with the digital, plus the digital noise leaking into those same amplifiers from the high-frequency digital circuits and computers housed in the same box.    That's part of the reason for preferring a true pure analogue system.    

 

As I said, purists will disagree with me.

If done properly (and I don't think it's hard) no one will ever pick that you have an AD/DA in the chain. Of course, once you tell them ….

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7 minutes ago, aussievintage said:

 

... plus the digital noise leaking into those same amplifiers from the high-frequency digital circuits and computers housed in the same box.

 

 

How does "digital noise leak into those same amplifiers from the high-frequency digital circuits ", av?

 

Is it only if they are in the same box?

 

Andy

 

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4 minutes ago, sir sanders zingmore said:

 

As I said, purists will disagree with me.

If done properly (and I don't think it's hard) no one will ever pick that you have an AD/DA in the chain. Of course, once you tell them ….

 

I am certainly going to give it a go.  After all, that rPi phono preamp  I have built will do the job, and it will only take a few minutes to reconfigure it for line in line out duty.   The software graphic eq is already there, currently used for linearising the magnetic cart signal.

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Just now, andyr said:

 

How does "digital noise leak into those same amplifiers from the high-frequency digital circuits ", av?

 

Is it only if they are in the same box?

 

Andy

 

 

They are in the same box.  Every DAC and ADC have analogue amplifiers/buffers in them. Proximity always makes it harder to screen out the digital noise from the analogue parts of the circuit, and the higher the frequency, the harder it gets.  You must recall the days of wanting to have external soundcards on computers to avoid picking up the digital noise from the computer.  Plenty of discussions around stereonet have spent much time on digital noise from computers and through digital interfaces.  High frequency sample rates and conversions and digital filtering,  all generate heaps of electronic noise.   Sure it can be done, as there are many good noise figures measured on DACs, but the same can be said of even the humble graphic equaliser, and they can be made purely analogue. Like the song says, "Anything you can do, I can do better"   So keep the digital circuitry non-existant, and filtering out the noise becomes a non-problem.

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On 24/12/2020 at 10:35 PM, aussievintage said:

 

They are in the same box.  Every DAC and ADC have analogue amplifiers/buffers in them. Proximity always makes it harder to screen out the digital noise from the analogue parts of the circuit, and the higher the frequency, the harder it gets.  You must recall the days of wanting to have external soundcards on computers to avoid picking up the digital noise from the computer.  Plenty of discussions around stereonet have spent much time on digital noise from computers and through digital interfaces.  High frequency sample rates and conversions and digital filtering,  all generate heaps of electronic noise.   Sure it can be done, as there are many good noise figures measured on DACs, but the same can be said of even the humble graphic equaliser, and they can be made purely analogue. Like the song says, "Anything you can do, I can do better"   So keep the digital circuitry non-existant, and filtering out the noise becomes a non-problem.

 

 

Aah, I see where you are coming from, av.  :thumb:

 

Andy

 

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On 24/12/2020 at 6:49 PM, sir sanders zingmore said:

 

I'm stretching my knowledge here but as far as a recall, the benefit of digital filters is that they can correct frequency without messing up phase (and indeed they can also correct phase). As far as I'm aware, analogue filters are unable to change frequency response without messing up phase response.

Plus you are putting a whole bunch of extra physical components in the signal chain which may add noise etc

 

 

Hello SSZ,

 

I agree with your posts in this thread. One other problem with those horrid analog equalisers, as I recall from the user manual of my early Behringer digital equalisers, is that, as shown below, the analog equaliser sums adjacent sliders in a way that the user didn’t intend. Whereas digital ‘graphic equaliser’ modules are usually designed to sum in a way that resembles the shape and magnitude of the sliders.

 

cheers

Grant

 

image.thumb.jpeg.329afc0e343b7bf29a4b76cc76b83afe.jpeg

(slider positions in soft grey)

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1 minute ago, Grant Slack said:

the analog equaliser sums adjacent sliders in a way that the user didn’t intend.

 

I take that into account.  It is actually a useful feature when you want to notch out a frequency that lies between two sliders. :) 

 

2 minutes ago, Grant Slack said:

Whereas digital ‘graphic equaliser’ modules are usually designed to sum in a way that resembles the shape and magnitude of the sliders.

Yes, as you say 'usually'.  However, in the software world, there are many different plugins available (vst ladspa etc) and many options that all behave differently depending on how the algo in them was written. Some (maybe badly written) can exhibit other strange effects never seen in the analogue world. Again, it is best to learn how they operate and take it into account when setting an eq.  Struck this a lot when using software to linearise a cartridge output to simulate loading effects in my phono eq project.

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