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Basic preamps wanted
I need a small, simple preamp to tailor the output of a standard
electret mic, to limit the bandwidth to approximately a telephone, say 300 - 3400 Hz and with fairly sharp cutoff. Must be available quickly, I haven't time to design and build. If the project works I will need several. Most simple off-the-shelf preamps do not have tone controls, or are large and unnecessarily complex for my purpose. Google hasn't been my friend so far. Any ideas? Thanks. |
Basic preamps wanted
"JohnTurd" I need a small, simple preamp to tailor the output of a standard electret mic, to limit the bandwidth to approximately a telephone, say 300 - 3400 Hz and with fairly sharp cutoff. Must be available quickly, I haven't time to design and build. If the project works I will need several. Most simple off-the-shelf preamps do not have tone controls, or are large and unnecessarily complex for my purpose. Google hasn't been my friend so far. Any ideas? ** Still waiting for the Tooth Fairy to arrive with your money ??? JESUS !!! Where DO all these stinking ****HEADS come from ???? ?? ..... Phil |
Basic preamps wanted
"Brian Gaff" wrote in message
om... This may or may not be a daft question here, but.. If the system is of restricted bandwidth, would not this fact do the job, or do you get funny effects with wider bandwidth signals. Cannot say that feeding nice quality down grotty phone lines sounds any less grotty if band limited or not. The nasty bodgit design inc solution is a high value capacitor in series with the mic and a vvery ngative feedbacked op amp for the amp which will maybe not be as noise free as it could be though. Brian The problem is that John hasn't told us what the application is, so we don't know what sort of performance he is looking for, nor do we know the reason for asking for a telephone bandwidth. We don't know what sort of budget he has either. He says he doesn't have the time to design and build, yet in fact reserching for a commercial product to perform this could take him far longer! Ordinary tone controls will not, of course, simulate a telephone bandwidth with any kind of accuracy. Telephone band filters exist, they have been used for many years, originally in front of modulators for FDM cable systems and more recently in front of voice codecs for digital systems, but these are industrial products not readily available in small quantities. David. |
Basic preamps wanted
On Mon, 6 Jul 2009 08:17:31 +0100, "David Looser"
wrote: "Brian Gaff" wrote in message . com... This may or may not be a daft question here, but.. If the system is of restricted bandwidth, would not this fact do the job, or do you get funny effects with wider bandwidth signals. Cannot say that feeding nice quality down grotty phone lines sounds any less grotty if band limited or not. The nasty bodgit design inc solution is a high value capacitor in series with the mic and a vvery ngative feedbacked op amp for the amp which will maybe not be as noise free as it could be though. Brian The problem is that John hasn't told us what the application is, so we don't know what sort of performance he is looking for, nor do we know the reason for asking for a telephone bandwidth. We don't know what sort of budget he has either. He says he doesn't have the time to design and build, yet in fact reserching for a commercial product to perform this could take him far longer! Ordinary tone controls will not, of course, simulate a telephone bandwidth with any kind of accuracy. Telephone band filters exist, they have been used for many years, originally in front of modulators for FDM cable systems and more recently in front of voice codecs for digital systems, but these are industrial products not readily available in small quantities. Thanks for the comments. What I am trying to do is to optimise a voice signal in the presence of high background noise levels, so I need a fairly sharp bandpass filter. I have of course tried simple RC sections for HPF and LPF but this is not sufficiently sharp for the purpose. |
Basic preamps wanted
On Mon, 06 Jul 2009 10:39:03 +0100, JohnT wrote:
On Mon, 6 Jul 2009 08:17:31 +0100, "David Looser" wrote: "Brian Gaff" wrote in message .com... This may or may not be a daft question here, but.. If the system is of restricted bandwidth, would not this fact do the job, or do you get funny effects with wider bandwidth signals. Cannot say that feeding nice quality down grotty phone lines sounds any less grotty if band limited or not. The nasty bodgit design inc solution is a high value capacitor in series with the mic and a vvery ngative feedbacked op amp for the amp which will maybe not be as noise free as it could be though. Brian The problem is that John hasn't told us what the application is, so we don't know what sort of performance he is looking for, nor do we know the reason for asking for a telephone bandwidth. We don't know what sort of budget he has either. He says he doesn't have the time to design and build, yet in fact reserching for a commercial product to perform this could take him far longer! Ordinary tone controls will not, of course, simulate a telephone bandwidth with any kind of accuracy. Telephone band filters exist, they have been used for many years, originally in front of modulators for FDM cable systems and more recently in front of voice codecs for digital systems, but these are industrial products not readily available in small quantities. Thanks for the comments. What I am trying to do is to optimise a voice signal in the presence of high background noise levels, so I need a fairly sharp bandpass filter. I have of course tried simple RC sections for HPF and LPF but this is not sufficiently sharp for the purpose. The just make a multiple pole filter using op-amps. There are plenty of cook book style recipes to do this. The usual way to maximise speech intelligibility would be, as you say, a pass band of 300Hz to 3kHz (approx), but between those extremes, you should have a 6dB per octave rise to accentuate the top end. The Texas Instruments web site knowledge base section offers interactive filter design pages that will do what you need. I'm sure that every other op amp designer has similar application notes. d |
Basic preamps wanted
In article 4a53c6a2.2006077968@localhost, Don Pearce
wrote: On Mon, 06 Jul 2009 10:39:03 +0100, JohnT wrote: Thanks for the comments. What I am trying to do is to optimise a voice signal in the presence of high background noise levels, so I need a fairly sharp bandpass filter. I have of course tried simple RC sections for HPF and LPF but this is not sufficiently sharp for the purpose. The just make a multiple pole filter using op-amps. There are plenty of cook book style recipes to do this. The usual way to maximise speech intelligibility would be, as you say, a pass band of 300Hz to 3kHz (approx), but between those extremes, you should have a 6dB per octave rise to accentuate the top end. That is so. I use cookbooks for such purposes. FWIW I've put some of the simpler design rules on the web at http://www.st-andrews.ac.uk/~www_pa/...rt3/page2.html The snag is that we still don't know the signal levels, impedances, etc, that would suit John's requirements. Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
Basic preamps wanted
In article ,
JohnT wrote: Thanks for the comments. What I am trying to do is to optimise a voice signal in the presence of high background noise levels, so I need a fairly sharp bandpass filter. I have of course tried simple RC sections for HPF and LPF but this is not sufficiently sharp for the purpose. Better way might be to use a noise cancelling mic. -- *I almost had a psychic girlfriend but she left me before we met * Dave Plowman London SW To e-mail, change noise into sound. |
Basic preamps wanted
In article 4a53c6a2.2006077968@localhost,
Don Pearce wrote: The just make a multiple pole filter using op-amps. There are plenty of cook book style recipes to do this. The usual way to maximise speech intelligibility would be, as you say, a pass band of 300Hz to 3kHz (approx), but between those extremes, you should have a 6dB per octave rise to accentuate the top end. I'd go up to approx 4.5Hz. Same as AM transmitters. The 'presence' frequencies help with clarity. -- *Young at heart -- slightly older in other places Dave Plowman London SW To e-mail, change noise into sound. |
Basic preamps wanted
On Mon, 06 Jul 2009 11:32:27 +0100, Jim Lesurf
wrote: That is so. I use cookbooks for such purposes. FWIW I've put some of the simpler design rules on the web at http://www.st-andrews.ac.uk/~www_pa/...rt3/page2.html The snag is that we still don't know the signal levels, impedances, etc, that would suit John's requirements. Well, given the job it is to do, I doubt that levels are important unless they are so high they cause overload - easily dealt with. And for impedances, my normal way is to make the input high and the output low; you seldom go far wrong that way. d |
Basic preamps wanted
"JohnT" "David Looser" The problem is that John hasn't told us what the application is, so we don't know what sort of performance he is looking for, nor do we know the reason for asking for a telephone bandwidth. We don't know what sort of budget he has either. He says he doesn't have the time to design and build, yet in fact reserching for a commercial product to perform this could take him far longer! Ordinary tone controls will not, of course, simulate a telephone bandwidth with any kind of accuracy. Telephone band filters exist, they have been used for many years, originally in front of modulators for FDM cable systems and more recently in front of voice codecs for digital systems, but these are industrial products not readily available in small quantities. Thanks for the comments. What I am trying to do is to optimise a voice signal in the presence of high background noise levels, so I need a fairly sharp bandpass filter. ** Very likely, that is a 100% wrong assertion. Obtaining good voice intelligibility from a microphone used in high noise environments is a problem that was SOLVED about 70 years ago. One simply buys or creates a "noise cancelling" microphone. http://en.wikipedia.org/wiki/Noise-canceling_microphone Two mics in one really, one picks up the voice plus nosie the other the noise only. Subtraction produces a result that is largely ambient noise free. ..... Phil |
Basic preamps wanted
On Mon, 06 Jul 2009 11:27:54 GMT, (Don Pearce) wrote:
On Mon, 06 Jul 2009 11:32:27 +0100, Jim Lesurf wrote: That is so. I use cookbooks for such purposes. FWIW I've put some of the simpler design rules on the web at http://www.st-andrews.ac.uk/~www_pa/...rt3/page2.html The snag is that we still don't know the signal levels, impedances, etc, that would suit John's requirements. Well, given the job it is to do, I doubt that levels are important unless they are so high they cause overload - easily dealt with. And for impedances, my normal way is to make the input high and the output low; you seldom go far wrong that way. There are plenty of circuits available, and yes I could buy in the components and make them up. But charging my time to do this will make the result too expensive for the customer. It would be cheaper to buy these: http://www.behringerdownload.de/FBQ8...Info_Rev_A.pdf which are really too good for the job. But in the absence of anything simpler, that is what I will do. |
Basic preamps wanted
On Mon, 06 Jul 2009 12:04:57 +0100, "Dave Plowman (News)"
wrote: In article , JohnT wrote: Thanks for the comments. What I am trying to do is to optimise a voice signal in the presence of high background noise levels, so I need a fairly sharp bandpass filter. I have of course tried simple RC sections for HPF and LPF but this is not sufficiently sharp for the purpose. Better way might be to use a noise cancelling mic. This is true, but I am assuming he doesn't have access to the source, and is trying to make the best of what he is receiving. Somewhere in a junk box I have a pair of throat mics that used to do service in a Lancaster bomber. They are quite uncanny - you could use them next to a revving F1 car, and hear nothing but the voice. The big problem is that they don't catch any kind of sibilant, so you have to be careful what words you say if you want to be understood. d |
Basic preamps wanted
"Don Pearce Congenital IDIOT" "Dave Plowman" Better way might be to use a noise cancelling mic. This is true, but I am assuming he doesn't have access to the source, and is trying to make the best of what he is receiving. ** Funny that the OP's first post starts out like this: " I need a small, simple preamp to tailor the output of a standard electret mic, to limit the bandwidth to approximately a telephone.. " He has access to the source signal and mic. Dickhead. .... Phil |
Basic preamps wanted
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Basic preamps wanted
Yeah, I know, , many years ago when I could see made one out of an old 741
op amp. Crap signal to noise, but you could reall tailor the responce very well with cheap components, and end up with a healthy output. As you say, its intriguing why pre grottification might be needed! Brian -- Brian Gaff - Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! "David Looser" wrote in message ... "Brian Gaff" wrote in message om... This may or may not be a daft question here, but.. If the system is of restricted bandwidth, would not this fact do the job, or do you get funny effects with wider bandwidth signals. Cannot say that feeding nice quality down grotty phone lines sounds any less grotty if band limited or not. The nasty bodgit design inc solution is a high value capacitor in series with the mic and a vvery ngative feedbacked op amp for the amp which will maybe not be as noise free as it could be though. Brian The problem is that John hasn't told us what the application is, so we don't know what sort of performance he is looking for, nor do we know the reason for asking for a telephone bandwidth. We don't know what sort of budget he has either. He says he doesn't have the time to design and build, yet in fact reserching for a commercial product to perform this could take him far longer! Ordinary tone controls will not, of course, simulate a telephone bandwidth with any kind of accuracy. Telephone band filters exist, they have been used for many years, originally in front of modulators for FDM cable systems and more recently in front of voice codecs for digital systems, but these are industrial products not readily available in small quantities. David. |
Basic preamps wanted
Have you looked into some of the add on devices used by ham radio folk to
tailor the sound either in the outgoing or incoming audio sections? Sounds like your needs are more akin to this group of users than prof audio ones. Brian -- Brian Gaff - Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. Blind user, so no pictures please! "JohnT" wrote in message ... On Mon, 6 Jul 2009 08:17:31 +0100, "David Looser" wrote: "Brian Gaff" wrote in message .com... This may or may not be a daft question here, but.. If the system is of restricted bandwidth, would not this fact do the job, or do you get funny effects with wider bandwidth signals. Cannot say that feeding nice quality down grotty phone lines sounds any less grotty if band limited or not. The nasty bodgit design inc solution is a high value capacitor in series with the mic and a vvery ngative feedbacked op amp for the amp which will maybe not be as noise free as it could be though. Brian The problem is that John hasn't told us what the application is, so we don't know what sort of performance he is looking for, nor do we know the reason for asking for a telephone bandwidth. We don't know what sort of budget he has either. He says he doesn't have the time to design and build, yet in fact reserching for a commercial product to perform this could take him far longer! Ordinary tone controls will not, of course, simulate a telephone bandwidth with any kind of accuracy. Telephone band filters exist, they have been used for many years, originally in front of modulators for FDM cable systems and more recently in front of voice codecs for digital systems, but these are industrial products not readily available in small quantities. Thanks for the comments. What I am trying to do is to optimise a voice signal in the presence of high background noise levels, so I need a fairly sharp bandpass filter. I have of course tried simple RC sections for HPF and LPF but this is not sufficiently sharp for the purpose. |
Basic preamps wanted
"Brian Goof" Have you looked into some of the add on devices used by ham radio folk to tailor the sound either in the outgoing or incoming audio sections? ** None of which are of ANY use when the noise originates at the mic diaphregm. In such cases, two way radio users employ "noise cancelling" mics. Dickhead. ..... Phil |
Basic preamps wanted
JohnT wrote:
There are plenty of circuits available, and yes I could buy in the components and make them up. But charging my time to do this will make the result too expensive for the customer. It would be cheaper to buy these: http://www.behringerdownload.de/FBQ8...Info_Rev_A.pdf which are really too good for the job. But in the absence of anything simpler, that is what I will do. Suggestion...find out what your customer really wants. For example.... I've recently completed work for a client who wanted some audio networks for training groups of students in comms protocols. One part of the spec was for a restricted frequency range. They wanted it to sound like a "radio comms network". My solution was very very simple and pragmatic, consisting of nothing more than a judicious choice of feedback and coupling capacitors among a few basic op amps. I didn't even bother to check the overall frequency response until my prototypes sounded "right". My client was not interested in numbers, he just wanted a certain sound quality and I provided it. It was a very cheap solution in terms of components and design time and the client was delighted with the results. After the first system was delivered he came back and ordered two more. BTW, thanks to those in here who gave me valuable advice when I was clueless at the start of this work some six months back...you know who you are ;-) |
Basic preamps wanted
"TonyL" BTW, thanks to those in here who gave me valuable advice when I was clueless ** Got some news for you - pal. YOU are still, 100%, ****ing clueless. ...... Phil |
Basic preamps wanted
On Tue, 7 Jul 2009 10:45:22 +0100, "TonyL"
wrote: Suggestion...find out what your customer really wants. For example.... I do know *exactly* what the customer wants, which is to eliminate low- and high-frequency machinery noise from an operator's microphone. I have ordered the FBQ8000 which are probably overkill but are guaranteed to do the job and are much cheaper than I would charge for my time in building something suitable. Thanks to everyone for their help. |
Basic preamps wanted
"JohnTurd" Suggestion...find out what your customer really wants. For example.... I do know *exactly* what the customer wants, which is to eliminate low- and high-frequency machinery noise from an operator's microphone. ** ********. The machine noise that is interfering with speech intelligibility is in the same band as the voice - filtering will not help. Have neither of you DICKHEADS ever noticed how easily a phone conversation is affected by ambient noise? I have ordered the FBQ8000 which are probably overkill ** Total waste of money. There IS one born every minute... . ...... Phil |
Basic preamps wanted
On Wed, 8 Jul 2009 11:41:08 +1000, "Phil Allison"
wrote: "JohnTurd" Suggestion...find out what your customer really wants. For example.... I do know *exactly* what the customer wants, which is to eliminate low- and high-frequency machinery noise from an operator's microphone. ** ********. The machine noise that is interfering with speech intelligibility is in the same band as the voice - filtering will not help. Have neither of you DICKHEADS ever noticed how easily a phone conversation is affected by ambient noise? I have ordered the FBQ8000 which are probably overkill ** Total waste of money. There IS one born every minute... . ..... Phil Have you tried engaging your diseased brain before opening your stinking cess-pit of a mouth? As it happens, I have done a full spectrum analysis of the audio from that microphone. The worst components are between 100 - 250 Hz, and these peak at 6dB above the voice. Then there are a range of components between 1 - 10 kHz which are all about the same peak level as the voice. Also the existing system is a bit low on gain. By putting in suitable filtering I can remove all of the heavy noise below the voice band and remove the rubbish above it. Yes, the in-band components will remain, but I have done a number of tests using recordings of the audio with a graphic equaliser on a PC, and careful filtering *greatly* increases readability - the customer was most impressed. I cannot get access to the mic, which is built into an equipment panel. The customer cannot accept machine downtime to facilitate a rebuild, so I can only play with the audio further down the line. This is my last comment on the matter, so now you can F**K OFF and get the serious medical treatment that you so urgently need. |
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