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#2712636 - 08/11/15 09:00 PM transparency and noise in mixer preamps
Rob Nold Offline
Member

Registered: 02/04/12
Posts: 11
Loc: Missouri
Hi Ethan, First off, Thanks for writing your excellent book "The audio expert"! I am about halfway through reading it and I consider it to be one of the best books on audio that I have ever read! On page 158 you mention your preference for transparency in a preamp. You also mention that you use a Mackie 1402vlz mixer for preamps on the front end of your recording setup. Do the preamps in the Mackie meet the criteria of having a "response is within .1 dB from 20 Hz to 20 KHz, and the sum of all distortion and noise is 80 dB or more below the signal"? Where did you find the specs to determine the transparency and noise floor of the Mackie xdr preamps? One more question; I currently have a Soundcraft mixer with GB30 preamps. The manual doesn't appear to have specs that are adequate to help me determine the transparency and noise floor of these preamps. An internet search isn't yielding much for me either. Do you have a suggestion on where I might obtain the specs necessary to determine the transparency and noise floor of the GB 30 preamps? Thanks in advance for your help! Rob


Edited by Rob Nold (08/12/15 07:58 AM)

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#2712796 - 08/12/15 11:18 AM Re: transparency and noise in mixer preamps [Re: Rob Nold]
Ethan Winer Moderator Offline
MP Hall of Fame Member

Registered: 06/12/00
Posts: 8905
Loc: New Milford, CT, USA
Those are great questions Rob. I can't seem to find the printed manual for my original Mackie 1202 mixer, but I do have a PDF for the next model they made, the 1202 VLZ. The specs are very good:

Noise varies between -84.5 and -100 depending on volume control settings. Distortion (1 KHz) is 0.0007 percent, which equates to -103 dB. Since there are no transformers or tubes in this mixer, I don't expect the distortion to increase too much at higher and lower frequencies. The response is +0 / -1 dB (though not -0.1), from 20 Hz to 20 KHz. So that's good enough for me. In use my 20+ year old Mackie 1202 sounds fine, and I'm sure it's not the limiting factor for making clean sounding recordings.

I'll add that when I bought a Focusrite Scarlett 8i6 converter a few years ago, I compared the noise and distortion of its preamps to my Mackie. The Scarlett was about 10 dB better for both noise level and distortion artifacts, as viewed on an FFT display in Sound Forge. But I decided to keep my Mackie 1202 in the path because it has better routing, such as letting me use an Aux bus to send reverb to a performer's earphones without recording the reverb. And other useful features.

As for your Soundcraft mixer, I found these specs online which confirm better than 1 dB response and better than 80 dB noise worst case:

http://soundcraft.com.s3.amazonaws.com/downloads/brochures/Soundcraft-GBSeries-Brochure.pdf

--Ethan

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#2712955 - 08/13/15 06:49 AM Re: transparency and noise in mixer preamps [Re: Ethan Winer]
Speedskater Offline
Member

Registered: 02/06/15
Posts: 18
Loc: Cleveland, Ohio, USA
I don't put much stock in manufacture's specs. For some mfg's the spec is just boilerplate and their units measure much better than the spec. With other mfg's the spec reflects the best unit in the warehouse measured under perfect conditions.


Edited by Speedskater (08/13/15 06:49 AM)
_________________________
Kevin

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#2713023 - 08/13/15 10:52 AM Re: transparency and noise in mixer preamps [Re: Speedskater]
Ethan Winer Moderator Offline
MP Hall of Fame Member

Registered: 06/12/00
Posts: 8905
Loc: New Milford, CT, USA
^^^ I agree with this, though most gear these days is good enough to not be the limiting factor. When someone complains in an audio forum that their mixes suck, and asks what "gear" they should buy next, what they probably need is more experience or maybe mixing lessons from a pro.

--Ethan

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#2714329 - 08/18/15 05:36 PM Re: transparency and noise in mixer preamps [Re: Ethan Winer]
Rob Nold Offline
Member

Registered: 02/04/12
Posts: 11
Loc: Missouri
Thanks for your replies everyone! I have another question. According to the frequency response specs for the Soundcraft it says: Mic/Line Input to any output, 20Hz - 20kHz ...... <1dB.

"Any output" would include the main 2 bus. Apparently, the frequency response is <1dB at the main 2 bus. Would the output at the insert point be a substantial improvement over the main 2 bus because there is less gain staging? If so, are we likely getting substantially less than 1 dB in terms of frequency response at the insert point output? Thanks again for your help! Rob


Edited by Rob Nold (08/18/15 06:40 PM)

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#2714342 - 08/18/15 06:20 PM Re: transparency and noise in mixer preamps [Re: Ethan Winer]
Griffinator Offline
TPS cook & bottle washer
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Registered: 03/28/02
Posts: 20318
Loc: Lynchburg, VA, USA
Originally Posted By: Ethan Winer
^^^ I agree with this, though most gear these days is good enough to not be the limiting factor. When someone complains in an audio forum that their mixes suck, and asks what "gear" they should buy next, what they probably need is more experience or maybe mixing lessons from a pro.

--Ethan


Actually, from my experience, the tracking room makes all the difference. Setting up a bunch of mattress eggcrates in your basement and pressing "record" doesn't generally yield good results in the final mix.

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#2714722 - 08/20/15 11:00 AM Re: transparency and noise in mixer preamps [Re: Rob Nold]
Ethan Winer Moderator Offline
MP Hall of Fame Member

Registered: 06/12/00
Posts: 8905
Loc: New Milford, CT, USA
Originally Posted By: Rob Nold
Would the output at the insert point be a substantial improvement over the main 2 bus because there is less gain staging?


The only way to know for sure is to call them and ask, or measure it yourself. But I have to tell you that -1 dB at 20 KHz is not something worth losing sleep over.

--Ethan

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#2715635 - 08/24/15 07:01 PM Re: transparency and noise in mixer preamps [Re: Ethan Winer]
Rob Nold Offline
Member

Registered: 02/04/12
Posts: 11
Loc: Missouri
Thanks Everyone! I think I have a general grasp of the answers to the frequency response questions for the Soundcraft preamps. Now about the noise. I see in your book Ethan that noise is one of the four parameters of audio fidelity. What I'm not seeing in the book is how to translate numbers like "80 db. noise worst case" into layman's terms? I have 2 other preamps--An A-designs Pacifica, and a LaChapell 992e.g. I just looked up the noise specs for each of them. The Pacifica is rated at (EIN) -128 dB. and the LaChapell is typically about (EIN)-125 dB. So I guess these two preamps have a fairly similar noise floor. And I'm assuming they're quieter than the Soundcraft pre's. Could someone please help me translate these numbers into layman's terms or tell me where to find this information in "The Audio Expert" Thanks again for all the help! Cheers! Rob


Edited by Rob Nold (08/24/15 07:04 PM)

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#2715637 - 08/24/15 07:25 PM Re: transparency and noise in mixer preamps [Re: Rob Nold]
Rob Nold Offline
Member

Registered: 02/04/12
Posts: 11
Loc: Missouri
Okay, I found it on page 160. So it appears that the Soundcraft pre's have quite a bit more noise than the Pacifica or the LaChapell. So what is the theoretical limit for low noise floor in a preamp?

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#2715660 - 08/25/15 12:21 AM Re: transparency and noise in mixer preamps [Re: Rob Nold]
Julf Offline
Senior Member

Registered: 03/08/13
Posts: 191
Loc: Amsterdam, The Netherlands
Originally Posted By: Rob Nold
So what is the theoretical limit for low noise floor in a preamp?


The theoretical limit depends on the source impedance and room temperature, but in practice 130 dB is about as good as you can get - and that is way better than the SNR of any source material. A vinyl LP has a SNR of maybe 70 dB, a CD a theoretical undithered 96 dB, but I really haven't come across any recordings with more than maybe 80 dB.

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#2715792 - 08/25/15 01:14 PM Re: transparency and noise in mixer preamps [Re: Julf]
Ethan Winer Moderator Offline
MP Hall of Fame Member

Registered: 06/12/00
Posts: 8905
Loc: New Milford, CT, USA
Julf has the right answer, though I imagine most LP records are closer to 55-60 dB. And that's for a clean LP with no clicks and pops. I also agree that most sources are worse than the -96 dB you get from 16-bit recording. I almost always record at 16 bits, and the source noise is always worse than the noise of the media.

Noise specs are tricky to assess for a variety of reasons. One reason is it's an easy spec to fudge. The Soundcraft noise is spec'd with a source impedance of 150 Ohms, and -128 dB EIN is good. Do you know what source the others were spec'd using? If this was my purchase, I wouldn't discount the Soundcraft over this spec if it otherwise meets my needs.

When I was writing my Audio Expert book a good friend of mine, John Roberts who's a very knowledgeable circuit designer, told me that even budget preamps these days can get to within a few dB of the theoretical minimum noise. He said the difference between a $30 preamp channel and a $2,000 preamp channel is only 1 or 2 dB.

--Ethan

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#2715909 - 08/25/15 09:18 PM Re: transparency and noise in mixer preamps [Re: Ethan Winer]
Griffinator Offline
TPS cook & bottle washer
20k Club

Registered: 03/28/02
Posts: 20318
Loc: Lynchburg, VA, USA
Yep. This is a situation where tech has exceeded esoterica by and large - the differences between an expensive preamp and a cheap one are in reliability (somewhat) and specific sound character (mostly), not noise floor or other problems that plagued cheap gear in the past.

(edit)

This isn't a recommendation to run out and buy a B******r piece of crap - there is a functional limit at which cheap starts to become true garbage, but well-built costs some money, and esoteric costs vast amount of money.

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#2715931 - 08/26/15 01:15 AM Re: transparency and noise in mixer preamps [Re: Griffinator]
Julf Offline
Senior Member

Registered: 03/08/13
Posts: 191
Loc: Amsterdam, The Netherlands
Yes, it is ironic that these days, a piece of cheap of mid-price kit is more likely to be transparent than some super expensive "high end" stuff...

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#2716027 - 08/26/15 11:05 AM Re: transparency and noise in mixer preamps [Re: Julf]
Ethan Winer Moderator Offline
MP Hall of Fame Member

Registered: 06/12/00
Posts: 8905
Loc: New Milford, CT, USA
Personally I prefer gear that's as clean as possible. If I want to add distortion or other color, I'd rather do that while mixing when I can hear all the pieces together in context. I don't want to pay extra for gear that adds color!

--Ethan

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#2788586 - 07/02/16 06:40 PM Re: transparency and noise in mixer preamps [Re: Ethan Winer]
Rob Nold Offline
Member

Registered: 02/04/12
Posts: 11
Loc: Missouri
Hi Ethan & others! I'd like to re-visit this subject. Thanks again for all of the previous replies! Since my last post, I've gone to using the Soundcraft GB-30 mic preamps almost exclusively and I'm not using color preamps as much these days. I am very happy with the results. Like others, I have come to the conclusion that I typically prefer transparency over color in a preamp. I'd like to take a look at the noise specs on the GB-30 as I find myself working with passive ribbon mics a lot these days and I'm wondering how close to the theoretical limit the GB-30's are in terms of noise? Upon re-visiting the link that Ethan posted above I found this information on noise which I had previously missed:

Mic E.I.N. @ unity gain,150 ohm source impedance ........................... -128dBu

I'm assuming when they say Mic E.I.N. that tapping the mic preamp at the insert point would yield this spec. which is the only way that I can access the signal coming directly from the mic preamps on my particular console. The GB 30's seem to be about the quietest preamps I have found yet. Are there substantially quieter preamps out there? or is this about as good as it gets? I have found other preamps that have nearly identical specs but seem to have a lot higher noise floor than the GB-30's in practice even though the manufacturer claims to be using 150 ohm source impedance. Do I have to disregard all manufacturers noise specs entirely and measure it myself? My biggest question is whether or not the published Soundcraft specs are legitimate useable numbers and also whether or not I'm going to be able to lower my noise floor. I would really like to hear from experienced users of Soundcraft GB-30 mic preamps on this matter. Thanks in advance for all help!


Edited by Rob Nold (07/03/16 08:46 AM)

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#2788649 - 07/03/16 03:58 PM Re: transparency and noise in mixer preamps [Re: Rob Nold]
Rob Nold Offline
Member

Registered: 02/04/12
Posts: 11
Loc: Missouri
I am embarrassed that I posted the above. I must have missed some previous replies that have the answers I need. So I guess the GB 30's are approaching the theoretical limits on low noise floor.

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#2788933 - 07/05/16 09:49 AM Re: transparency and noise in mixer preamps [Re: Rob Nold]
Ethan Winer Moderator Offline
MP Hall of Fame Member

Registered: 06/12/00
Posts: 8905
Loc: New Milford, CT, USA
No need to be embarrassed! Yes, that's close to the theoretical limit of thermal noise for a given temperature.

Note that while this forum is still present, mostly as an archive, I set up a new forum that I post in more often:

Ethan's Audio Expert Forum

--Ethan

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Moderator:  Ethan Winer