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RIAA inverting
tinpanalley
post Aug 25 2013, 18:42
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I'm capturing a bunch of my 78s. I'm following along all the proper steps and applying proper curves for different labels.
Maybe I'm nuts, but applying the RIAA inverted curve invariably has the effect in EVERY case, no matter the label of the record, of worsening the sound to the point where it has so much high-end that idiosyncrasies of the low end are completely lost. Can anyone explain why this is the case?
I get that the RIAA curve is an electronic recording element that is erroneously placed on a 78 by capturing it into a contemporary system and that reversing it gets us to the purer signal, but why would that make it sound worse than even the live record?
Thought, guidance? I'd love to understand this.
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AndyH-ha
post Aug 25 2013, 19:30
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The RIAA EQ is the standard adopted for LPs. Before this, most labels had their own unique EQ. Essentially every disk had something applied upon writing to the disk master. Undoing the RIAA EQ applied by a modern phono preamp to any of these earlier recordings is only half the process. You must then apply the correct EQ to obtain a flat frequency response.

The RIAA EQ, and probably all the others that were one time in use, have a significant roll-off of highs to compensate for the way a cartridge works, producing a higher level signal for a faster moving stylus. Reversing the RIAA EQ thus increases the high end to the same extent that it is (properly, for an LP) reduced by the preamp.


And increasing the bass to compensate for the (relatively) slow stylus movement at low frequencies.

This post has been edited by AndyH-ha: Aug 25 2013, 19:31
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AndyH-ha
post Aug 25 2013, 19:42
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I don't know about the text of the article, not having read it, but I think the curves are dsiplayed correctly here.
http://www.smartdevicesinc.com/riaa.html
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tinpanalley
post Aug 25 2013, 19:48
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Yes, I'm aware of the different label curves. I apply those as well, that helps but there is often still missing low end. And no I'm not expecting it to sound like contemporary bass heavy music. I know a lot about these early recordings. I just wonder how other reputable CD remasters achieve a certain bass levels. Do you think they EQ them to sound better on stereos because most people would find the original sound tinny?
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AndyH-ha
post Aug 25 2013, 22:13
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I don't know just what other people do exactly but I know from comments that it often involves adjustments by ear. The article I referenced above goes into some detail about recording and cutting practices and factors that effected frequency response. Some of that goes well beyond static EQ curves by label.
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Glenn Gundlach
post Aug 26 2013, 09:52
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You do not need to 'remove' the RIAA curve. If you know what the curve is supposed to be you subtract the RIAA from it and apply the difference. If the record EQ is unknown you will have to do it by ear until you're satisfied. I believe you'll find it only needs a few dB boost / cut at the extremes.

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DVDdoug
post Aug 26 2013, 18:45
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QUOTE
I'm following along all the proper steps and applying proper curves for different labels.
Maybe I'm nuts, but applying the RIAA inverted curve invariably has the effect in EVERY case, no matter the label of the record, of worsening the sound to the point where it has so much high-end that idiosyncrasies of the low end are completely lost. Can anyone explain why this is the case?
That is exactly what will happen if you play the record without equalization. When you apply the inverted curve, you are essentially (re)applying the recording curve (without any playback compensation).

There are two or three ways to do this -
Assuming you are using a standard phono preamp with RIAA EQ...

You can remove the RIAA EQ, and add the special 78 EQ. (Make sure you are applying the playback curve, not the recording curve. The recording curve boosts highs and cuts lows, and of course the playback curve does the opposite.)

Or, you can leave the RIAA EQ and apply the difference,

Or you can leave the RIAA EQ, and adjust by ear.
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tinpanalley
post Jan 10 2014, 14:10
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I just noticed now that someone had replied here. I guess my notification didn't work. Thanks for replying everyone.

QUOTE (DVDdoug @ Aug 26 2013, 12:45) *
When you apply the inverted curve, you are essentially (re)applying the recording curve (without any playback compensation).

Sorry, I didn't understand this. I think I may need to hear it a bit more simply. Sorry that I'm not well versed enough but I'm trying to master this.

QUOTE (DVDdoug @ Aug 26 2013, 12:45) *
There are two or three ways to do this -
Assuming you are using a standard phono preamp with RIAA EQ...
...I am, yes.

QUOTE (DVDdoug @ Aug 26 2013, 12:45) *
You can remove the RIAA EQ, and add the special 78 EQ. (Make sure you are applying the playback curve, not the recording curve. The recording curve boosts highs and cuts lows, and of course the playback curve does the opposite.)
I thought I made that clear, sorry. This is precisely what I've been doing: removing RIAA and applying the special EQs for each different label. And I get the ultra high end and no low end sound that is not right to my ears.
QUOTE (DVDdoug @ Aug 26 2013, 12:45) *
Or, you can leave the RIAA EQ and apply the difference,
Or you can leave the RIAA EQ, and adjust by ear.
What difference? And if you can go one way or the other then why is everyone so adamant about reversing the RIAA curve?

Thanks!!
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pdq
post Jan 10 2014, 14:58
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QUOTE (DVDdoug @ Aug 26 2013, 12:45) *
When you apply the inverted curve, you are essentially (re)applying the recording curve (without any playback compensation).

That's not quite right. The RIAA equalization curve actually consists of two separate components.

When the master is cut, lateral displacement of the groove is proportional to amplitude. The RIAA recording compensation boosts the high frequencies somewhat to allow a corresponding reduction of those high frequencies, along with noise, on playback.

However, on playback the signal amplitude from the cartridge is proportional to velocity, not displacement. This creates a six dB per octave increase of amplitude with frequency. Most of the playback compensation is compensating for this relationship.

So as you can see, the recording compensation curve is quite different from the inverted playback compensation curve. (Some graphs here would probably make this much clearer, but I don't have the time.)
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2Bdecided
post Jan 10 2014, 15:28
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Are you intending to re-run your previous five page thread on this topic on this tinpanalley? wink.gif

http://www.hydrogenaudio.org/forums/index....c=93659&hl=

Cheers,
David.
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tinpanalley
post Jan 10 2014, 16:04
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Touché, 2B. blush.gif
I did consciously not want to repeat my post and if I touched on things already discussed there, I'm sorry to have wasted anybody's time. I just tend to assume that if I have a question STILL about something that it's something I didn't get an explanation for before so I ask what I think is a new question. But of course, as time passes, one forgets things and I should perhaps revisit my old questions before posting new ones.

That being said, if I remember correctly, that thread was about asking how to clean up my 78 captures with very little knowledge of how to do it, having read a lot but not practiced much. Now I find myself listening to things I captured months ago and wondering why CDs mastered by experts/archivists in the field of early jazz 78 recordings have more resonance and bass than the ones I've made even, in some cases, when I've got a cleaner disc than they have to begin with. Surely they know about inverting the RIAA curve and applying a label-specific curve, so why do they get such rich sound understanding that they definitely aren't producing CDs for mainstream consumption or pop music. Does my assumption make sense?
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2Bdecided
post Jan 10 2014, 16:34
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from that thread...

QUOTE (2Bdecided @ Mar 14 2012, 10:49) *
Yes, I usually find the "correct" curve to be lacking in bass. Not always, but mostly. Some re-issues of 78s (especially some American ones from the 1970s/80s) boost the bass by a ridiculous amount.

It's quite hard to judge by ear though. Do the best you can, but keep the previous version in case you decide you can do better later (e.g. when you change stereo or headphones).

FWIW I find it really difficult because I'm so used to listening to my records with the RIAA curve applied. It's only through the PC that I have access to the correct curves. I can hear that the treble especially is more natural with it corrected, but it's not what I'm used to from my favourite records.

You never posted any audio samples, so I've no idea what you're hearing. For me, with the correct curve I still think the treble is at the right level, but drowned in clicks, while the bass is too light. Hence after tweaking I end up with something closer to RIAA than the "correct" curve, by reducing the treble and increasing the lower bass. For quick-and-dirty listening I've found it's easier to just use RIAA and boost part of the upper-midrange (around 1.5kHz - 3kHz, shallow Q).

Cheers,
David.

This post has been edited by 2Bdecided: Jan 10 2014, 16:37
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Juha
post Jan 10 2014, 22:24
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If you could post some 78rpm record audio sample (30sec limit here) recorded with RIAA correction and if possible another audio sample (from same recording) which represents the target result.
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2Bdecided
post Jan 13 2014, 11:19
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I think that's a good idea. It sounds like tinpanalley already has a particular track in mind.
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Juha
post Jan 13 2014, 18:12
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QUOTE (tinpanalley @ Aug 25 2013, 20:42) *
... Maybe I'm nuts, but applying the RIAA inverted curve invariably has the effect in EVERY case, no matter the label of the record, of worsening the sound to the point where it has so much high-end that idiosyncrasies of the low end are completely lost. Can anyone explain why this is the case?


If you used Audacity (FIR) EQ preset for inverting then you should know that there were some issues with the preset when I made some comparisons back in 2009.

http://www.hydrogenaudio.org/forums/index....showtopic=74336

I checked the situation now and found out that the EQ preset is now improved but ... the result is still different from the result got using RIAA EQ (IIR) plug-ins which I have prepared in the past. http://jiiteepee.tripod.com/home.html

I have not followed the Audacity developement so I can't tell the exact version # which had this fix included.

This post has been edited by Juha: Jan 13 2014, 18:13
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tinpanalley
post Jan 13 2014, 19:08
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Sorry everyone. I'll be back with some audio samples soon. This is a particularly bad time but I'll be by in the next few days. However, Juha, yes I was using the Audacity v 1.3.13 beta to apply the inverse RIAA curve. I do all the other curve applying using Brian Davies' Equalizer.
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