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Author Topic: Comments concerning upcoming test in Chicago...  (Read 27553 times)

crm0922

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Re: Comments concerning upcoming test in Chicago...
« Reply #15 on: November 04, 2005, 06:31:57 PM »

Do RADAR and PTHD have analog trims to allow the reference level to be set without the need to attenuate the signal from tape?  I don't use either of those formats regularly, but in my experience, when stuff comes from tape the "soft boundary" can allow big transients to exceed 15db from nominal.  This works on tape, but will result in "overs" in the digital rigs.

If that is the case, you either lower the output level from the output of the tape machine, attenuate it with the console or something, or trim down the inputs on the digital device if it has such feature.  Many converters do not, or if they do they are internal and shouldn't be messed with in ordinary discourse.

Hmm...  If you set up the oscillator for +4dbU and align the tape to that, it should come in somewhere near -15dbFS if the tone is passed through at unity.  So in order to make "all things equal", one would have to either reduce the output from tape for both listening tests, or correct the difference later by matching output levels when the dump is already complete (if "overs" were ocurring).

Very curious about the results, especially Fletcher, MM, and SA's opinions on RADAR vs. Alsihad with the same material.

Chris
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RKrizman

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Re: Comments concerning upcoming test in Chicago...
« Reply #16 on: November 04, 2005, 06:58:15 PM »

crm0922 wrote on Fri, 04 November 2005 18:31

Do RADAR and PTHD have analog trims to allow the reference level to be set without the need to attenuate the signal from tape?  I don't use either of those formats regularly, but in my experience, when stuff comes from tape the "soft boundary" can allow big transients to exceed 15db from nominal.  This works on tape, but will result in "overs" in the digital rigs.




The HD 192 has dual trim pots for each input and each output analog channel. Each channel can have 2 different trim levels stored which may be chosen between by the software. (this is in addition to +4 versus -10 option)

Also, FWIW, according to the 192 manual:

" In +4 dBu operating mode, the 192 I/O is  a 24-bit digital audio device capable of producing audio signals up to +26 dBu across +4 dBu input/output.  The default headroom value is 18 dB.  This translates to a maximum output of +22 dBu."

Keep in mind also that it's not just a question of digital overs.  If you slam the analog electronics too hard and they harsh out there is no fuzzy tape saturation to mitigate the blow.

-R
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djui5

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Re: Comments concerning upcoming test in Chicago...
« Reply #17 on: November 04, 2005, 07:15:08 PM »

Please don't print to Pro-Tools at -16. -18 is the optimal calibration level.

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Curve Dominant

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Re: Comments concerning upcoming test in Chicago...
« Reply #18 on: November 05, 2005, 01:29:21 AM »

CWHumphrey wrote

Most PT systems I've used have been setup for -18dBfs. It's same old argument we used to have with the dat machines. Do you push up the operating level to use up as many bits as possible?


I would guess no, not with PTHD's noise floor, which seems sufficiently deep to handle -18dBfs.

Mr. Kashiwa should weigh in on this, and he will, no doubt.

My concern was that -15dBfs (initially suggested by Mr. Albini) seemed just a tad overboard. Perhaps not for analog, mind you, but we're testing for PROPER transfer, bearing in mind optimal use of said kit, are we not? IOW: We don't want to turn this into a "See what happens when we abuse the kit..." sort of thing, do we?

This whole issue of  "push up the operating level to use up as many bits as possible" is really a relic of outdated digital gear with its (previously) low bitrates and flawed A/D convertor designs - none of which should be applied to today's paradigms, not to mention be imposed on this testing procedure. Right?

Pending Gannon's input, I propose we settle on a -18dBfs transfer.

CWHumphrey

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Re: Comments concerning upcoming test in Chicago...
« Reply #19 on: November 05, 2005, 04:13:35 AM »

Curve Dominant wrote on Sat, 05 November 2005 06:29

CWHumphrey wrote

Most PT systems I've used have been setup for -18dBfs. It's same old argument we used to have with the dat machines. Do you push up the operating level to use up as many bits as possible?


My concern was that -15dBfs (initially suggested by Mr. Albini) seemed just a tad overboard. Perhaps not for analog, mind you, but we're testing for PROPER transfer, bearing in mind optimal use of said kit, are we not? IOW: We don't want to turn this into a "See what happens when we abuse the kit..." sort of thing, do we?

This whole issue of  "push up the operating level to use up as many bits as possible" is really a relic of outdated digital gear with its (previously) low bitrates and flawed A/D convertor designs - none of which should be applied to today's paradigms, not to mention be imposed on this testing procedure. Right?

Pending Gannon's input, I propose we settle on a -18dBfs transfer.


I asked the question, where was Mixerman's operating level in PT when experienced the issue in question?  Some engineers are still reaching for the top of the digital scale. I don't do that anymore, but at one time, I was very much a disciple of that theory.  I repented on the 2nd Rod Stewart standards album, after having a look at the VU meters on the SSL E that we were using for monitoring (yep, we were mixing ITB).  Since then, I'm a big fan of 0VU--again.  

I think it would be a mistake not check it out at various operating levels

-Carter
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Bob Olhsson

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Re: Comments concerning upcoming test in Chicago...
« Reply #20 on: November 05, 2005, 11:28:58 AM »

Isn't there a global switch in a 192 that lets you instantly change its input or output levels? That would speed up comparisons considerably.

The challenge is that we are dealing with a system. How easy is the console for the tape machine to drive vs. the 192 and what is the overload point of the tape returns? Different consoles and tape machines are likely to produce different results. I've experienced a particular console (MCI 500) where the low frequency problem was obvious and another particular console (SSL 9K) where it wasn't.

J.J. Blair

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Re: Comments concerning upcoming test in Chicago...
« Reply #21 on: November 05, 2005, 12:36:23 PM »

Carter, I still think you could have brought the strings up 3/4 of a db.
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Fletcher

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Re: Comments concerning upcoming test in Chicago...
« Reply #22 on: November 05, 2005, 02:26:10 PM »

Moved from the "methodology" thread...

kensluiter wrote on Sat, 05 November 2005 01:29

If you don't minding me chiming in,

I believe it makes sense , as Fletcher suggests, to make the transfer at a couple of different calibration levels on the 192's; but I think it would be a real mistake not to make one of those levels -18dbfs.

Over the years (since 1992, in fact), I have experienced and observed engineers shift from the -14dbfs=0 VU "use all the available bits" method, to the more conservative -20dbfs=OVU "unity gain" approach.

In the two cities/markets I've worked in (Chicago and LA) it seems the -18dbfs has become the informal standard.

I think Steve Albini's involvement in this certainly helps validate the process, but no one I know who make records w/ PTHD aligns the converters to -15dbfs as he is suggesting doing.


I also strongly believe that the hi-res rough mixes (both from tape and PT playback) should be printed back into the 192's.
I'm not arguing that the Prism converter isn't a better converter than the 192; but I think playback of the multitrack while resolving from one clock whilst printing thru converters that are resolved to another seperate clock will give the tape playback an unfair advantage.  If you use two seperate clocks (one for the Prism, one for the 192) even though the mix is being generated in the analog domain; will smear the audio on the PT mix.

If I was mixing a record, I would probably resolve one to the other, but for this purpose, I wouldn't do anything that would make the 192 behave any differently than it would if it was running off it's own internal clock.



I was talking about doing the test using the internal clock, then a couple of different external clocks to see if they make a difference... it was just a thought.

I am working from the presupposition that there is going to be a pretty large difference when the audio is played back from tape and when the audio is played back from PT... and less of a difference when the audio is played back from RADAR... so, my question [at least one of the questions I have] is whether these differences will stem from the analog electronics in both units [converters], or if this difference will stem from the clocking source.

One of the questions I believe this will answer is whether the audio from PT can be improved with an external clocking source... like the clock from a RADAR or Apogee "Big Ben", etc.

As for the -18dbfs headroom thing... fine with me.  I would probably have suggested 14 & 20... but 14 and 18 would work.

We could also go for 18 and 24 as far as I'm concerned... but I would like to walk in with a solid and agreed upon methodology for the levels at which these tests are recorded... I DO NOT want this particular arguement/discussion/whatever you want to call it while we're all standing in the middle of a control room.

This needs to be agreed upon well in advance of the test(s) performed.
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compasspnt

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Re: Comments concerning upcoming test in Chicago...
« Reply #23 on: November 05, 2005, 02:45:48 PM »

Personally, I would see -14 as not important.

Preference here would be -18, -20, perhaps -24 just to see.
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rnicklaus

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Re: Comments concerning upcoming test in Chicago...
« Reply #24 on: November 05, 2005, 03:48:44 PM »

I believe anytime there is a transfer going on from any format to any format that one has to be ready for anything and be a problem solver.

Years ago, I had a terrible problem with a 2" to 2" transfer.

I believe that was a Delany Bramlett record where there were 2 producers.

We all cut the basic tracks and had settled on 2" 16 track as it was going to be a R&R record.

The project grew - 2 drummers horns strings way too much stuff.

As I went on to mix another record, the project went to a very prominent LA studio and one producer decided to xfer the project to 2" 24 track (this was '77 or '78) and do some overdubs.

A few weeks later I am back on the project and push play on the new tape and I could not believe what I was seeing and hearing.

The original tracks were cut where the kick and snare would kiss  0 VU (250 alignment) the bass was sitting at 0 - you get the picture.

The new tape with new important overdubs had the original tracks that were transferred peaking, best case, at -7!  I was all about WTF?

I call the studio that did the xfer and told them about it and of course they claimed that the original multitrack was recorded that way - and they say it was xfered over as recorded.  Of course I told them no way.

It turns out the way they had the xlr patch bay in the back of the room was in addition to both machines connecting to the console so there was the huge load on the system when both machines were patched together. (trying to remember that long ago)

When I had them bring up the original tape without both machines being patched together, the levels were as I recorded them.  With both machines patched to each other, the level fell almost 10DB.

They never noticed this or questioned it and I assume never looked at tones.

From that point on I will never take any kind of transfer for granted if I see or hear anything close to off in any way.

Just a thought as this test comes together.



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Bob Olhsson

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Re: Comments concerning upcoming test in Chicago...
« Reply #25 on: November 05, 2005, 05:18:25 PM »

FWIW SMPTE did a massive research project to determine an optimum, idiot-proof digital audio transfer level for broadcasters. What they came up with was 185x+4VU = -20 dBFS. at 20 bits.

Unfortunately it turned out a lot of consoles didn't have enough headroom to operate at -20 (potentially +26-+30 dBM analog peaks) and a lot of gear manufacturers didn't want to spring for line drivers and power supplies capable of bulletproof performance at that level.

So where we're at is that best case, digital gear needs to be aligned to the limitations of the analog gear it is being used with. Worst case the analog circuit of some digital gear isn't up to working optimally with some analog gear.

The Resonater

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Re: Comments concerning upcoming test in Chicago...
« Reply #26 on: November 05, 2005, 08:20:13 PM »

Fletcher wrote on Sat, 05 November 2005 19:26

I was talking about doing the test using the internal clock, then a couple of different external clocks to see if they make a difference... it was just a thought.


One of the questions I believe this will answer is whether the audio from PT can be improved with an external clocking source... like the clock from a RADAR or Apogee "Big Ben", etc.


RE: the clocking of the various devices...as you probably know, Dan Lavry swears up and down that nearly all digital devices work optimally when using the internal clocks.  FWIW...

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RKrizman

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Re: Comments concerning upcoming test in Chicago...
« Reply #27 on: November 05, 2005, 09:10:49 PM »

Fletcher wrote on Sat, 05 November 2005 14:26

I am working from the presupposition that there is going to be a pretty large difference when the audio is played back from tape and when the audio is played back from PT... and less of a difference when the audio is played back from RADAR... so, my question [at least one of the questions I have] is whether these differences will stem from the analog electronics in both units [converters], or if this difference will stem from the clocking source.




First, I wouldn't presuppose that at all.  Secondly, if there is a problem it might stem from the interface between the devices, as Bob O has suggested.

-R
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RKrizman

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Re: Comments concerning upcoming test in Chicago...
« Reply #28 on: November 05, 2005, 09:14:12 PM »

Fletcher wrote on Sat, 05 November 2005 14:26


We could also go for 18 and 24 as far as I'm concerned... but I would like to walk in with a solid and agreed upon methodology for the levels at which these tests are recorded... I DO NOT want this particular arguement/discussion/whatever you want to call it while we're all standing in the middle of a control room.

This needs to be agreed upon well in advance of the test(s) performed.



That's fine, but realize that in the act of doing this if you are getting digital overs then you have to back it down, no matter what levels you decided on in advance, otherwise you're just misusing the equipment.  So I'd add that contingency to your methodology.

Should this be in the methodology thread?

-R

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malice

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Re: Comments concerning upcoming test in Chicago...
« Reply #29 on: November 05, 2005, 11:21:08 PM »

The Resonater wrote on Sun, 06 November 2005 02:20


RE: the clocking of the various devices...as you probably know, Dan Lavry swears up and down that nearly all digital devices work optimally when using the internal clocks.  FWIW...




Except devices with bad clock in them.

malice
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