Hybrid analog/digital preamp?

scott wurcer · 15th February 2004, 11:47 AM

With the speed and availability of digital processing power, I was thinking that a simple one stage preamp with maybe one of the RIAA time constants feeding a DSP programmed to do the rest would be an interesting project. I'm sort of thinking out loud over my morning coffee.

netgeek · 15th February 2004, 03:26 PM

Perhaps such a thing could be one part of a whole family of dedicated widgets??? (e.g. the AD1954 or some of the alesis products). It would be great to see more dedicated "black box" type devices that could be easily integrated by "non-dsp designers"......

Hey, if you had some "in" at a place like Analog Devices I'll bet you could make it happen..........

Meanwhile, I'm still waiting for my AD1954 samples to play with.

Regards,
Bill

dwk123 · 17th April 2004, 05:08 PM

Came across this old post randomly, but this hybrid approach is something I've been thinking about as well since recording my vinyl to cd/dvd is a project on my todo list.
I've actually been thinking about a fully-digital approach where you just run the 'table through ~60dB of gain and apply the full RIAA digitally, but I just can't bring myself to believe that this is optimal - I'm not sure you end up with enough S/N performance in the treble after applying the filters. OTOH the midrange and treble will be at a (relatively) higher level before digitizing so you (in theory) get more 'bits' of resolution on the initial capture than when using an already-corrected signal.
The idea of applying the 50Hz section in the preamp to get 'into the ballpark' and then correcting digitally seems to be a promising idea - the phono 'pre' can be much simpler (ie cheaper) than a full RIAA approach, and you only need moderate digital correction to complete the eq.

One of the big practical factors might be the ability to handle pops/ticks - recording a pre-equalized signal will result in much lower energy from pops/clicks than if you record the un-equalized signal, which might help to avoid clipping during recording.

Anyone actually end up trying this or something similar?

EC8010 · 21st April 2004, 01:08 PM

Quote:

Originally posted by dwk123
The idea of applying the 50Hz section in the preamp to get 'into the ballpark' and then correcting digitally seems to be a promising idea - the phono 'pre' can be much simpler (ie cheaper) than a full RIAA approach, and you only need moderate digital correction to complete the eq.

Exactly. A low-pass 3180us filter (shelving at 3.18us) would equalise the velocity response of the transducer, and the fiddly 318us, 75us could be done very precisely with digits.

jan.didden · 21st April 2004, 01:18 PM

Scott,

I would be worried about loosing quality by going ADC - DSP - DAC.

Anyway, purist LP/vinyl lovers would probably come after you with a hatchet for this blasphemy.

Jan Didden

jan.didden · 21st April 2004, 01:22 PM

Reply to myself: I can probably try that out easily with my Behringer Ultradrive Pro 2496, which surely has the required filter options. All that is needed is a flat pre ahead of it. And a turntable, of course. So, how about taking a RIAA preamp, removing the correction stuff (maybe leave in the 3.18uS low pass), leaving a flat gain block, and sticking its output in a Behringer?

Jan Didden

dwk123 · 22nd April 2004, 02:42 PM

Quote:

Originally posted by janneman
Scott,

I would be worried about loosing quality by going ADC - DSP - DAC.

Anyway, purist LP/vinyl lovers would probably come after you with a hatchet for this blasphemy.

Jan Didden

Well, the idea really only makes sense in the context of digitizing vinyl in the first place. I've ended up going with a completely digital system (using the Panasonic Digital receivers and homebrew digital xovers), and so recording the vinyl at 24/96 and burning to DVD-V is probably my best practical compromise.

I'd agree that deliberately introducing a spurious AD/DA cycle is pretty pointless.

Onvinyl · 22nd April 2004, 06:02 PM

Quote:

Anyway, purist LP/vinyl lovers would probably come after you with a hatchet for this blasphemy.

Vinyl Lovers are well-balanced, kind and peaceful people, I think they won't

Quote:

I'd agree that deliberately introducing a spurious AD/DA cycle is pretty pointless.

We-ell, but think about recordings with different/historic filtering, well performing analog solutions with switchable filter curves are quiet expensive, so a programmable system with memory banks can be quíet advantageous!

Rüdiger

scott wurcer · 22nd April 2004, 07:15 PM

I'm trying to borrow one of our new AD1940 DSP development
systems to give it a crack real time, maybe with some fancy tick and pop interpolation too.

15th February 2004, 11:47 AM	#1
scott wurcer diyAudio Member Join Date: Jan 2004 Location: cambridge ma	Hybrid analog/digital preamp? With the speed and availability of digital processing power, I was thinking that a simple one stage preamp with maybe one of the RIAA time constants feeding a DSP programmed to do the rest would be an interesting project. I'm sort of thinking out loud over my morning coffee.

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15th February 2004, 03:26 PM	#2
netgeek diyAudio Member Join Date: Nov 2003 Location: East Coast USA	Perhaps such a thing could be one part of a whole family of dedicated widgets??? (e.g. the AD1954 or some of the alesis products). It would be great to see more dedicated "black box" type devices that could be easily integrated by "non-dsp designers"...... Hey, if you had some "in" at a place like Analog Devices I'll bet you could make it happen.......... Meanwhile, I'm still waiting for my AD1954 samples to play with. Regards, Bill

17th April 2004, 05:08 PM	#3
dwk123 diyAudio Member Join Date: Feb 2002	Came across this old post randomly, but this hybrid approach is something I've been thinking about as well since recording my vinyl to cd/dvd is a project on my todo list. I've actually been thinking about a fully-digital approach where you just run the 'table through ~60dB of gain and apply the full RIAA digitally, but I just can't bring myself to believe that this is optimal - I'm not sure you end up with enough S/N performance in the treble after applying the filters. OTOH the midrange and treble will be at a (relatively) higher level before digitizing so you (in theory) get more 'bits' of resolution on the initial capture than when using an already-corrected signal. The idea of applying the 50Hz section in the preamp to get 'into the ballpark' and then correcting digitally seems to be a promising idea - the phono 'pre' can be much simpler (ie cheaper) than a full RIAA approach, and you only need moderate digital correction to complete the eq. One of the big practical factors might be the ability to handle pops/ticks - recording a pre-equalized signal will result in much lower energy from pops/clicks than if you record the un-equalized signal, which might help to avoid clipping during recording. Anyone actually end up trying this or something similar?

21st April 2004, 01:18 PM	#5
jan.didden diyAudio Member Join Date: May 2002 Location: Great City of Turnhout, Belgium Blog Entries: 6	Scott, I would be worried about loosing quality by going ADC - DSP - DAC. Anyway, purist LP/vinyl lovers would probably come after you with a hatchet for this blasphemy. Jan Didden

21st April 2004, 01:22 PM	#6
jan.didden diyAudio Member Join Date: May 2002 Location: Great City of Turnhout, Belgium Blog Entries: 6	Reply to myself: I can probably try that out easily with my Behringer Ultradrive Pro 2496, which surely has the required filter options. All that is needed is a flat pre ahead of it. And a turntable, of course. So, how about taking a RIAA preamp, removing the correction stuff (maybe leave in the 3.18uS low pass), leaving a flat gain block, and sticking its output in a Behringer? Jan Didden

22nd April 2004, 07:15 PM	#9
scott wurcer diyAudio Member Join Date: Jan 2004 Location: cambridge ma	I'm trying to borrow one of our new AD1940 DSP development systems to give it a crack real time, maybe with some fancy tick and pop interpolation too.