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Post by swurveman on Sept 1, 2016 8:24:29 GMT -6
What preamps are you guys with low impedance mics using? I have a pair of schoeps cmc mics (35 Ohms) and need a good low impedance preamp. The KM84 has an imedance of 50 Ohms. So, for anybody using them I'd be interested in which pre you're using for acoustics.
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Post by Guitar on Sept 1, 2016 9:35:03 GMT -6
I always liked the Lo-Z setting on the UA Solo 610. Not sure if that helps you or not. You can also lower the impedance of any mic preamp with a simple resistor network. Naiant sells some pre-made ones for a low price.
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Post by svart on Sept 1, 2016 9:48:27 GMT -6
Impedance matching is for optimizing power transfer across frequency. What usually results from poor matching is increasing "standing waves" across the frequency spectrum, which could cause some frequency anomalies, but usually not in the audio spectrum unless something is really, really wrong.
However, this is lossy, with about 50% efficiency (half signal loss!).
Most systems like a slight impedance mismatch, in favor of the driving side being lower impedance than the receiver side (sometimes called impedance bridging). This optimizes voltage transfer and provides signal damping. Your source should always be the lower impedance number, with the receiver being the higher number.. Just like guitar amps.
Honestly though, if you're not having any real issues, then there is no reason to bother strictly adhering to classical impedance matching.
For experiment's sake you could try putting a 3dB or 6dB 600R attenuator between the mic and preamp and see if it changes anything besides the level..
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Post by swurveman on Sept 1, 2016 9:52:25 GMT -6
Impedance matching is for optimizing power transfer across frequency. What usually results from poor matching is increasing "standing waves" across the frequency spectrum, which could cause some frequency anomalies, but usually not in the audio spectrum unless something is really, really wrong. However, this is lossy, with about 50% efficiency. Most systems like a slight impedance mismatch, in favor of the driving side being lower impedance than the receiver side (sometimes called impedance bridging). This optimizes voltage transfer and provides signal damping. Honestly though, if you're not having any real issues, then there is no reason to bother strictly adhering to classical impedance matching. For experiment's sake you could try putting a 3dB or 6dB 600R attenuator between the mic and preamp and see if it changes anything besides the level.. I am having real issues with my high impedance preamps. I have to really crank the gain which increases noise. My other preamps, which I can toggle to 300 ohms are better, but I haven't been happy with the sound. Thanks for the tip! |
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Post by swurveman on Sept 1, 2016 9:53:12 GMT -6
I always liked the Lo-Z setting on the UA Solo 610. Not sure if that helps you or not. You can also lower the impedance of any mic preamp with a simple resistor network. Naiant sells some pre-made ones for a low price. Thanks for the tip. I'll check it out. |
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Post by svart on Sept 1, 2016 9:55:00 GMT -6
Impedance matching is for optimizing power transfer across frequency. What usually results from poor matching is increasing "standing waves" across the frequency spectrum, which could cause some frequency anomalies, but usually not in the audio spectrum unless something is really, really wrong. However, this is lossy, with about 50% efficiency. Most systems like a slight impedance mismatch, in favor of the driving side being lower impedance than the receiver side (sometimes called impedance bridging). This optimizes voltage transfer and provides signal damping. Honestly though, if you're not having any real issues, then there is no reason to bother strictly adhering to classical impedance matching. For experiment's sake you could try putting a 3dB or 6dB 600R attenuator between the mic and preamp and see if it changes anything besides the level.. I am having real issues with my high impedance preamps. I have to really crank the gain which increases noise. My other preamps, which I can toggle to 300 ohms are better, but I haven't been happy with the sound. Thanks for the tip! Lowering the receiver impedance should only lower the output of the mic.. The lower the "impedance" number of the preamp input means that you are increasing the loading on the mic. Schoeps have always been slightly low output though. |
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ericn
Temp
Balance Engineer
Posts: 14,978 
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Post by ericn on Sept 1, 2016 11:21:45 GMT -6
Impedance matching is for optimizing power transfer across frequency. What usually results from poor matching is increasing "standing waves" across the frequency spectrum, which could cause some frequency anomalies, but usually not in the audio spectrum unless something is really, really wrong. However, this is lossy, with about 50% efficiency (half signal loss!). Most systems like a slight impedance mismatch, in favor of the driving side being lower impedance than the receiver side (sometimes called impedance bridging). This optimizes voltage transfer and provides signal damping. Your source should always be the lower impedance number, with the receiver being the higher number.. Just like guitar amps. Honestly though, if you're not having any real issues, then there is no reason to bother strictly adhering to classical impedance matching. For experiment's sake you could try putting a 3dB or 6dB 600R attenuator between the mic and preamp and see if it changes anything besides the level.. Damn you Chris for coming up with a theroly scientific answer that explains it better before I can simply say Just try some different settings and see what works in each situation ! |
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Post by popmann on Sept 1, 2016 21:42:32 GMT -6
I'm thinking you're asking the wrong question.
If your preamps can't provide all the gain you need without noise, get new ones.
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Post by swurveman on Sept 2, 2016 7:23:10 GMT -6
I'm thinking you're asking the wrong question. If your preamps can't provide all the gain you need without noise, get new ones. I've never had to push the gain like that-wide open to get a -18dbfs signal- so I don't know if it was noise or ambience. It was a young girl playing an acoustic very gently. So, I should have moved the Schoeps mic closer. Before recording I didn't isolate the Schoeps and turn it up to hear the noise/ambience. Had I done that I would have heard the noise and acted to try to minimize the noise/ambiance. A tough learning lesson for me who tracks through headphones in a one room studio. It was a live performance situation, where I put one condenser mic in a figure 8 close to the guitar neck and an sm58 for the voice - with the schoeps ` 6-8 feet from the girl. I was hoping to get a good sound either from the mono Schopes or the two close mics. I got neither. It was my first time doing the figure 8 / sm58 thing and they were getting impatient. Not an ideal situation for one of the most difficult tracking tasks. It could have been ambient noise. I'll have to see. I moved my computer out of the room. but there still could be some ambient noise. I am treating the ceiling in the area where I recorded her with 19 GIK spot panels with diffusion, but I didn't have it completed and she wanted to come in anyway. I can make it sound decent, but I am on a quest to get a great acoustic guitar sound-which for me is a 70's sound that has warm lower mids and not skreechy mids or treble. I know the guitar/room/mics and placements are all part of this. So, still on the quest. Hoping the room treatment helps things greatly and bringing in someone to help spending hours experimenting. Thanks for your thoughts. |
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Post by Guitar on Sept 2, 2016 7:39:47 GMT -6
Maybe you could have put an omni mic right up on the guitar, since there would be no proximity effect in omni. Just another idea to add to the pile. Maybe some sort of de-noise plugin could save your existing track.
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Post by swurveman on Sept 2, 2016 7:57:33 GMT -6
Maybe you could have put an omni mic right up on the guitar, since there would be no proximity effect in omni. Just another idea to add to the pile. Maybe some sort of de-noise plugin could save your existing track. Thanks. I have a denoize plug. So, I'm going to do that. I'll try the omni. I thought it would be worse in this situation because it would add even more room, but I'll try it in my tests. My biggest hope is that the treatment is going to dramatically improve the sound. It's room/guitar/mic/preamp for acoustic guitar. I've got some good mics and preamps, but the room needed to be fixed. I can't control the quality of the guitar. I probably should buy a really good acoustic for people who come in with crappy acoustics. All it takes is money.... My acoustician did a tremendous job fixing my mix position problems. So, I'm hoping for the same gains in the tracking area. |
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Post by svart on Sept 2, 2016 8:17:29 GMT -6
Maybe you could have put an omni mic right up on the guitar, since there would be no proximity effect in omni. Just another idea to add to the pile. Maybe some sort of de-noise plugin could save your existing track. Thanks. I have a denoize plug. So, I'm going to do that. I'll try the omni. I thought it would be worse in this situation because it would add even more room, but I'll try it in my tests. My biggest hope is that the treatment is going to dramatically improve the sound. It's room/guitar/mic/preamp for acoustic guitar. I've got some good mics and preamps, but the room needed to be fixed. I can't control the quality of the guitar. I probably should buy a really good acoustic for people who come in with crappy acoustics. All it takes is money.... My acoustician did a tremendous job fixing my mix position problems. So, I'm hoping for the same gains in the tracking area. I put eyebolts in some of my 2'x4'x4" acoustic panels so I could mount them on mic stands. That way I can move them around and put them in strategic places around singers and/or acoustic players. It really helps close micing, without having to resort to changing the acoustics of the whole room. |
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Post by swurveman on Sept 2, 2016 9:42:36 GMT -6
Thanks. I have a denoize plug. So, I'm going to do that. I'll try the omni. I thought it would be worse in this situation because it would add even more room, but I'll try it in my tests. My biggest hope is that the treatment is going to dramatically improve the sound. It's room/guitar/mic/preamp for acoustic guitar. I've got some good mics and preamps, but the room needed to be fixed. I can't control the quality of the guitar. I probably should buy a really good acoustic for people who come in with crappy acoustics. All it takes is money.... My acoustician did a tremendous job fixing my mix position problems. So, I'm hoping for the same gains in the tracking area. I put eyebolts in some of my 2'x4'x4" acoustic panels so I could mount them on mic stands. That way I can move them around and put them in strategic places around singers and/or acoustic players. It really helps close micing, without having to resort to changing the acoustics of the whole room. Thanks. I've also got 3- 32″ x 72″ x 3″ GIK Screen panels. I also have 4' foot high array of Mio Room dividers which I've been told to line up to the right and left of the recording space. Hopefully, all those options with the ceiling treatment should give me lots of options. I need to do listening tests and understand and record what the tweaks/changes do. The day I am happy with an acoustic guitar recording will be a happy day. |
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Post by EmRR on Sept 2, 2016 15:34:32 GMT -6
I'm thinking you're asking the wrong question. If your preamps can't provide all the gain you need without noise, get new ones. I've never had to push the gain like that-wide open to get a -18dbfs signal- so I don't know if it was noise or ambience. It was a young girl playing an acoustic very gently. So, I should have moved the Schoeps mic closer. And sometimes it's beyond what physics will allow. I've recently had similar gentle player in, and the guitar sounds more like a harpsichord in the distance it's played so lightly. My notes on equipment settings look wrong; something around 80dB with a close condenser and signal levels still down around -24dBFS. It happens. I took to standing by my outer control window and noting times at which I heard traffic noise, some of which was over a block away. Never ever had to do that! A helicopter from the hospital 5 miles away went overhead somewhat nearby, and I could hear it in headphones for over 3 minutes, couldn't hear it by ear at all. If I remember correctly, in theory lower impedance equates to lower theoretical base noise limits. The mic already provides this low impedance source, the preamp can be noise optimized for any theoretical source Z as noise sources differ at varying impedances. Most preamps are optimized for a 150-200 ohm source, and a 50 ohm source is a bonus UNLESS that source is dynamic, low in output, and you can get slightly more 'free' gain from the right type of transformer input in the preamp (rare). Most preamps with impedance selection are not going to give you a better noise figure at a particular setting, they are either there for 1) proper loading of certain mics or 2) color palette. Transformer coupled preamps having true variable input impedance taps (rare) may optimize noise with some historical lower Z dynamic mics, they will only hurt a low-Z condenser by hobbling it's own headroom/distortion/output level. For example, you may get a better sound out of a WE/RCA/Shure ribbon that's set for 50 ohms if you have a transformer coupled preamp with unloaded secondary and a choice of 50/150/600 input taps if you set the preamp for 50 ohms, as the transformer gives more gain. That sound MAY be better than the mic and pre both set for 150 IF the pre transformer is better than the mic transformer. Still a lot of 'if's'. |
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