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Old August 1st, 2008, 09:00 AM   #1
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Appalling audio input on Sony A1P

I recently recorded a live classical music concert of just one violin & Piano. I used my favourite AKG 451's in a crossed pair feeding into a Sony A1P with the gain switch set to -10dB as necessitated by these high output mics. But even so, there was still the slight & occasional overload, but worse still, was the continuous background hiss from the very poor input stage on this camera. (mics about 1 - 2 metres from talent and less than 6 metres of cable to XLR inputs on camera).

I would expect a pro camera to be capable of accepting the input levels from pro mics. These mics are capable of producing output voltages in excess of one volt on closely miced loud sounds yet the appalling input stages on the Sony cameras overload at around 50mV. Dare I suggest this is to boost sales of "Sound Forge" !!

Has anyone else had similar problems or is it that I am the only person to use "pro" mics to capture high-quality sound, as the problem is reduced with lower output mics.

Surely it's time Sony engineers learned how to design a decent quiet mic input stage with a respectable overload margin as I have had similar experiences with earlier Sony pro cameras. (PDX-10 & PD 170)

What's up with these guys ?

This is not rocket science but simple application of some very basic electronics. I used to design high grade audio phono pre-amps 30 yrs. ago and getting good overload & low noise was no big deal way back then !

Comments please.

Ron Cooper.
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Old August 1st, 2008, 09:29 AM   #2
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It's a sad fact that the whole audio section of most cameras is just an afterthought of the designers who are generally focussed on image bells and whistles
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Old August 1st, 2008, 10:29 AM   #3
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I guess that's their assessment of the market. Us audio snobs are sort of left out of the prosumer video equipment revolution. They must be figuring that if it's good enough for dialog, it's good enough.

Of course some will dispute whether Sony's prosumer line of camcorders is good enough for dialog.

There has been a concurrent equipment revolution in the semi-pro music studio market that's brought us all sorts of audio goodies at low price.

But it seems that for good music recording there's no getting away from double-system sound. That really hasn't changed over the years, but the truely pro audio gear has gotten a little less expensive and much more reliable and consistent.

Short of that... To Ron's particular predicament, I wonder how much better this would work with a pair of 20db pads into the A1.
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Old August 1st, 2008, 03:25 PM   #4
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What are you peaking at on it's meters before distortion occurs?
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Old August 2nd, 2008, 07:33 AM   #5
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Thanks very much for your replies.

A pair of external 20 db pads would fix the overload problem but only exacerbate the noise situation as when you insert external pads you are also raising the input impedance at the XLR inputs which will degrade the S/N ratio further. Hence it is desirable to use the internal attenuators as these should not degrade but ACTUALLY IMPROVE the S/N ratio by altering the internal feedback circuit and also give a higher input overload margin. (Of course this is what you would expect from a properly designed input stage, - domestic or pro.)

As for the level meter reading it was under the zero mark and this is the real problem with poorly designed input stages as you can turn the input gain right down but the raw signal coming in from the mic is causing the input stage to overload BEFORE it gets to the gain control in the camera's input stage.

As I stated previously, preventing this is not rocket science but simple application of basic electronic design. Further, the cost of doing this is peanuts which I find quite baffling particularly on professional equipment.

RC.
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Old August 2nd, 2008, 11:52 AM   #6
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Quote:
Originally Posted by Ron Cooper View Post
...Further, the cost of (improving input stage design) is peanuts which I find quite baffling particularly on professional equipment....
Not in defense of Sony - I find it frustrating as well. In their world, an A1 is not "professional equipment". As we move out of Sony prosumer and into Sony broadcast I think we find better audio design.

Having said that, we end up using a product that is out of balance on visual capabilities vs. sound capabilities.
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Old August 2nd, 2008, 07:35 PM   #7
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In reality I think you're right Seth, but what a poor situation this is. My previous rant also applies to the PD 170 which I assumed to be a pro camera with a decent mic input. (How stupid of me !) Yes I would hope that the b'cast cameras are better but totally impractical for a prosumer like me who just wants decent results without too much fuss.

(As a good friend of mine says, "when you go on vacation you don't want to look like Channel nine on holiday ! "

Obviously XLR inputs are no guarantee of a pro camera, just a guarantee of a secure & very bulky mic connection ! - (Now Ron be thankful at least for that & don't get started on high quality 3 pin mini jacks !) Realistically though, with careful attention you can get very good sound via these inputs but you need to work at it, and, they have the advantage of simplicity light weight etc. In fact that is one reason I like the A1P as it gives you the freedom of totally removing the XLR adaptor & just go with the mini jack input which is what I use most of the time with a good external stereo mic on top.

RC.
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Old August 5th, 2008, 02:01 AM   #8
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Hiss

Yes, good old Sony! What might be worth checking out is that the phantom supply voltage to your AKG451s is in fact the full 48 volts. If only 12v is being supplied from the camera - or are you using a separate phantom supply box? - you get symptoms similar to those you describe.
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Old August 5th, 2008, 07:31 AM   #9
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Yes Nick I checked that too & it was OK but it doesn't matter greatly as the AKG 451's are very forgiving and will work down to 12v.

RC.
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