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KathyB · Posted: Tue Jan 13, 2009 11:00 am Post subject: Impedance with mic and preamp

Hi All!

I came across a post by Frank (Thanks Frank:-) that mentions a mic and preamp combination may reduce the output level by 6 dB. Exactly the problem I've had for quite a while now. I have been normalizing to compensate, but I'd really like to solve this another way.

Here's my set up: studio projects c-1 mic, Emu 0404usb preamp, symetrix 528E, Adobe Audition 2.0 on my compaq Presario.

And here's my question. Is the preamp a bad match for my mic and is it the weak link in my chain? If so, what are some good choice for a new one? I'd be willing to spend 3 or 4 hundred bucks on a new one if it'll solve this problem.

As always, thanks for generously sharing your ideas and experiences. I'm eagerly awaiting the day, when I have enough experience to answer someone's question on this board!!!

Kathy

Frank F · Posted: Tue Jan 13, 2009 12:06 pm Post subject:

Because the EMU is a Solid State pre-amp AND is USB powered; an underpowered USB port might be your problem initially. Another suggestion (considering you might be happy with the EMU) is to change your cables, not just the microphone cables, but the USB cable as well. Small changes can result in big audio differences.

IF you have the opportunity and still desire to purchase a new pre-amp might I suggest the Studio Projects VTB1. Not only is the VTB1 a good match with the C-1 microphone (nice mic) but it not under-powered as many USB devices are designed to be.

The EMU draws power from two sources - the +/- 5 volt power supply AND the USB port. If one part of the equation is underpowered the entire setup is "off". Since the EMU is a Solid State device, cranking the power is not ideal and usually results in distortion. Therefore the preamp has been designed to deliver nice sound, but a little under the accepted normal level output.

With a "tube" or analog pre-amp such as the VTB1, the device is more forgiving and can be powered to 100% (sometimes more than 100%) audio level (0 db) without distortion.

A little checking can net you a Studio Projects VTB1 for around $150.00 (more or less).

Toodles

F2
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KathyB · Posted: Tue Jan 13, 2009 1:02 pm Post subject:

Thanks Frank!! I have already changed the cables--all of them-- to no avail. I'm going to check into the VTB1 from Studio Projects.

Kathy

Edo · Guest

georgethetech · Posted: Tue Jan 13, 2009 3:38 pm Post subject:

As Edo said, check your signal chain.
The order should be:
1- studio projects c-1 mic
2- symetrix 528E,
3- Emu 0404usb preamp (line input)
4- compaq Presario

You should have no problem with gain this way.
Make sure Phantom Power is on (back of 528e). Gain (the first knob on the left) shouldn't need to be much higher than 12 o'clock.

If all of this mystifies you, PM me...
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Jeffrey Kafer · Posted: Tue Jan 13, 2009 4:14 pm Post subject:

Another note: make sure you're using the rear USB ports on your computer. The front ones are usually just a hub, and can introduce power problems.
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KathyB · Posted: Tue Jan 13, 2009 8:15 pm Post subject:

Thanks for all the comments. My signal chain is set up the correct way. (I just wrote it wrong in my post:-( Also, I am using the rear usb port.

Thanks for all your ideas.
Kathy

georgethetech · Posted: Tue Jan 13, 2009 8:51 pm Post subject:

Kathy:
I am a bit confused about what the problem is. Are you saying you can't get your levels hot enough in Audition, or that the gain structure is showing a loss of signal someplace? There is nothing wrong with peaking at -6db and normalizing later, that is certainly acceptable. Or do you mean you peak out at -6db and no matter what can't get any higher? That's another problem...
_________________
If it sounds good, it is good.
George Whittam
GeorgeThe.Tech
424-226-8528
VOBS.TV Co-host
TheProAudioSuite.com Co-host
TriBooth.com Co-founder

KathyB · Posted: Wed Jan 14, 2009 9:08 am Post subject:

George,

I can normalize in audition and that gets my work to sound OK. Here's my concern. The gain structure is showing a loss somewhere. If I turn the gain up, the wave form clips at -6.

I have searched for about a year--long time, huh--to try and figure out why this is happening. I came across this from one of Frank's posts a while ago. I am rewriting it here because I printed it out and saved it on my desk (literally) rather than saving the link.

Frank's advice:

"Look for the impedance factor when purchasing a pre-amp. Find the pre-amp which works best with your microphone. Matching microphone and pre-amp impedances to the same value (power-matching) is not necessarily desirable since it reduces both the level and the signal to noise ratio by 6 dB. For dynamic and condenser microphone, the preferred preamp input impedance is generally about ten times that of the microphone output."

That -6dB really rang a bell with me, which is why I started this thread. I'm really close to picking up the phone and calling to order the Studio Projects VTB1 that Frank recommends (right now it's not in stock at Sweetwater.) I checked on line. Of course I'm sure they'll get it for me as quickly as they can. I've done business with them before.

Honestly, I don't know much about the impedance factor, so I'm just grateful for Frank's advice and asking if anyone else has had experience with this problem.

Kathy

Bill Campbell · DC Joined: 09 Mar 2007 Posts: 621

The EMU 0404 has an excellent preamp in it, why do you need two preamps?
Just use the 0404 without the Symetrix.

The -6 clipping in Audition is a fairly common problem with some equipment.
There's been quite a few posts on the Adobe forums about it. Nobody seems to have a definitive answer on on why it happens.

Does it clip at -6 when you record in Stereo/two channel in AA?
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Frank F · Posted: Wed Jan 14, 2009 12:51 pm Post subject:

As noted in the Adobe forums: "Much of the DigiDesign or related products tend to underpower AA, resulting in clipping or a hard limiting at approximately 60%".

This is a design "flaw" with some equipment/pre-amps, as described earlier. The EMU is basically (now) an upgrade for the Sound Blaster products. This is good, and bad. Good as EMU products will continue to be excellent products and inexpensive, bad, because it tends to limit the next step in the EMU's evolution.

As Solid State pre-amp's go, Bill is correct - the EMU 0404 does have a good pre-amplifier section although it is purposefully designed with a lower level output section. Similar to those of M-Audio and DD products, this "flaw" from the IC "chip" keeps noise to a very minimum level and limits the voltage level from the equipment into the recording program.

Why use a different pre-amp with a good sound card - one word: QUALITY.

Have fun with what you have, then when what you have does not work - get a bigger hammer (or a new toy which does work)

Toodles

F2
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Be thankful for the bad things in life. They opened your eyes to the good things you weren't paying attention to before. email: thevoice@usa.com

Bill Campbell · DC Joined: 09 Mar 2007 Posts: 621

Frank and Kathy:

Do you think it might be "mis-matched" cabling? Balanced/unbalanced
issue. There's a few pieces of gear in the mix.
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Frank F · Posted: Wed Jan 14, 2009 5:16 pm Post subject:

Bill, here is a quote from above in the post: KathyB writes: "Thanks Frank!! I have already changed the cables--all of them-- to no avail."

F2
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Be thankful for the bad things in life. They opened your eyes to the good things you weren't paying attention to before. email: thevoice@usa.com

KathyB · Posted: Wed Jan 14, 2009 5:38 pm Post subject:

Thanks for all the advice! I described this problem to my salesman at sweetwater and he recommends this:

http://www.sweetwater.com/store/detail/MBox2Mini/

It comes with Pro Tools, which I know is really big in the industry, but may be overkill for my voiceover work.

I am seriously looking at getting a new toy and I'm still thinking the studio project VTB1 recommendation is the best for me. Any ideas?

Thanks again!
Kathy

chuckweis · Contributor IV Joined: 27 Feb 2008 Posts: 136