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#1
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What is "reverse gain"
I've heard of reverse gain as an indicator of gain through a device
connected "backwards", i.e. a signal is applied at the output pin of an op amp, and measured at the input pin, gain being measured-at-input divided by applied-at-output. But in the context of pro audio, specifically, microphones connected to mixers in a pro audio (live or recording) situation, what does "reverse gain structure" mean? |
#2
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What is "reverse gain"
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#3
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What is "reverse gain"
"But _this_ amplifier goes below 0."
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#4
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What is "reverse gain"
William Sommerwerck wrote: "But _this_ amplifier goes below 0." Might it also require signal inversion ? Graham |
#5
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What is "reverse gain"
"Eeyore" wrote ...
William Sommerwerck wrote: "But _this_ amplifier goes below 0." Might it also require signal inversion ? I remember an article in an April edition of "Popular Electronics" back in the late 1950s or early 1960s. It was a special April-Fools feature about "negative AC". They trumped up some impresive-looking formulae to show that if you took the - path of some +/- factor, you could create this "inverse power". They printed two photos demonstrating this power... 1. A soldering iron with ice-cicles hanging off the tip. 2. A gooseneck lamp with a cone of "black" coming out of the shade where the bulb had sucked up all the available light in the path. I wish I had kept the photos. |
#6
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What is "reverse gain"
I remember an article in an April edition of "Popular Electronics"
back in the late 1950s or early 1960s. It was a special April-Fools feature about "negative AC". It was more likely Radio-Electronics. Regardless, I'd like to see the article, too. |
#7
Posted to rec.audio.pro
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What is "reverse gain"
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#8
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What is "reverse gain"
Richard Crowley wrote:
I remember an article in an April edition of "Popular Electronics" back in the late 1950s or early 1960s. It was a special April-Fools feature about "negative AC". They printed two photos demonstrating this power... 1. A soldering iron with ice-cicles hanging off the tip. 2. A gooseneck lamp with a cone of "black" coming out of the shade where the bulb had sucked up all the available light in the path. I remember that from QST. The article was entitled "Contra Polar Energy." -- If you e-mail me and it bounces, use your secret decoder ring and reach me he double-m-eleven-double-zero at yahoo -- I'm really Mike Rivers ) |
#9
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What is "reverse gain"
I've heard of reverse gain as an indicator of gain through a device connected "backwards", in RF circuits you have forward gain S21 and reverse gain S12 also called reverse isolation. If an RF amplifers' reverse isolation apporaches it's forward gain, it is in danger of oscillation. These and other S paramters are measured with a network analyzer. I have never heard of the term reverse gain used in audio work. Maybe it could mean in a PA the gain (or loss) from the speaker back to the mic as an indicator of the possibility of feedback oscillation or maybe you meant RESERVE gain. Mark |
#10
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What is "reverse gain"
"Mark" wrote in message ... I've heard of reverse gain as an indicator of gain through a device connected "backwards", in RF circuits you have forward gain S21 and reverse gain S12 also called reverse isolation. If an RF amplifers' reverse isolation apporaches it's forward gain, it is in danger of oscillation. These and other S paramters are measured with a network analyzer. I have never heard of the term reverse gain used in audio work. Maybe it could mean in a PA the gain (or loss) from the speaker back to the mic as an indicator of the possibility of feedback oscillation or maybe you meant RESERVE gain. Mark see bi-directional amplifiers http://www.impactacoustics.com/produ...1008&sku=41033 in audio perhaps, reverse log attenuator: a pot that attenuates logarithmically as the pot is turned clockwise. excerpt from wikki: There is also an anti-log pot or reverse audio taper which is simply the reverse of a log pot. It is almost always used in a ganged configuration with a log pot, for instance, in an audio balance control. |
#11
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What is "reverse gain"
Richard Crowley wrote in message ... "Eeyore" wrote ... William Sommerwerck wrote: "But _this_ amplifier goes below 0." Might it also require signal inversion ? I remember an article in an April edition of "Popular Electronics" back in the late 1950s or early 1960s. It was a special April-Fools feature about "negative AC". And the power company has the nerve to charge you for the electrons that enter your house but then they suck em back out again?? |
#12
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What is "reverse gain"
Tim Perry wrote: "Mark" wrote I've heard of reverse gain as an indicator of gain through a device connected "backwards", in RF circuits you have forward gain S21 and reverse gain S12 also called reverse isolation. If an RF amplifers' reverse isolation apporaches it's forward gain, it is in danger of oscillation. These and other S paramters are measured with a network analyzer. I have never heard of the term reverse gain used in audio work. Maybe it could mean in a PA the gain (or loss) from the speaker back to the mic as an indicator of the possibility of feedback oscillation or maybe you meant RESERVE gain. see bi-directional amplifiers http://www.impactacoustics.com/produ...1008&sku=41033 in audio perhaps, reverse log attenuator: a pot that attenuates logarithmically as the pot is turned clockwise. excerpt from wikki: There is also an anti-log pot or reverse audio taper which is simply the reverse of a log pot. It is almost always used in a ganged configuration with a log pot, for instance, in an audio balance control. Or pan control or in a balanced mic amp gain stage (inter-emitter resistor). Incidentally, did you know that 'log' and 'anti-log' controls are named the wrong way round w.r.t. clockwise rotation ? Think about it. Graham |
#13
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What is "reverse gain"
wrote:
I've heard of reverse gain as an indicator of gain through a device connected "backwards", i.e. a signal is applied at the output pin of an op amp, and measured at the input pin, gain being measured-at-input divided by applied-at-output. But in the context of pro audio, specifically, microphones connected to mixers in a pro audio (live or recording) situation, what does "reverse gain structure" mean? There were (possibly still are) bi-directional 'repeaters' used on long telephone lines. The device was inserted into a standard impedance transmission line (usually of 600-ohms characteristic impedance) and was coupled into the line with a pair of 'hybrid' transformers. Between the transformer circuits were two amplifiers, one facing in each direction. The hybrid transformer was part of a bridge circuit which balanced the real line against a 'dummy line' made up of resistors and capacitors. When the hybrid was correctly nulled, the output of each amplifier was prevented from appearing in the input signal of the other, but each amplifier could see signals arriving from its own line. Thus gain in each direction was possible and, if one direction was regarded as 'forward', the gain in the opposite direction was 'reverse gain'. I doubt if this has any practical application to modern systems and equipment - at least, not at audio frequencies. -- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk |
#14
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What is "reverse gain"
I've heard of reverse gain as an indicator of gain through a device
connected "backwards", I haven't. Geez, where do we get these ideas? Must be a web site somewhere. Actually, one of the hybrid (h) parameters for junction transistors is the reverse voltage gain through the device. This does not apply, of course, to amplifier circuits. |
#15
Posted to rec.audio.pro
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What is "reverse gain"
On Dec 5, 8:45*pm, Mark wrote:
I've heard of reverse gain as an indicator of gain through a device connected "backwards", in RF circuits you have forward gain S21 and reverse gain S12 also called reverse isolation. * If an RF amplifers' reverse isolation apporaches it's forward gain, it is in danger of oscillation. *These and other S paramters are measured with a network analyzer. Yeah, that's how I've seen the term used. It's a pretty well-established term in some kinds of RF work, although not particulary common. Very low reverse gain is, of course, desirable, like -60dB or better (lower). If a device is properly designed, the number should be so low that it's never an issue, sort of like crosstalk. I have never heard of the term reverse gain used in audio work. Neither had I, until recently. The person who's using the term seems to be using as a strange way of saying that certain microphones provide a hotter than usual signal level, so you should turn the mic input trims down on the mixer (as compared to the trim settings more commonly used with other microphones). That's a pretty elementary concept: with a hotter mic signal level, back off the input trim. It's a typical part of setting up the gain structure in a pro audio system; by adusting the input trims. But the term "reverse gain structure" seems a strange way of describing it, and I had never heard it until recently. If it were me, I'd say something like, "these mics provide a pretty hot signal level, so you might want to back off the input trims." Yeah, it's related to gain structure, but I don't get where the "reverse" comes from. I suspect it's some kind of marketing mumbo-jumbo, but I thought I'd ask if anyone had ever heard the term. -- Warped |
#16
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What is "reverse gain"
Incidentally, did you know that 'log' and 'anti-log' controls are named the wrong way round w.r.t. clockwise rotation ? Think about it. Graham I don't wanna. it hurts my brain. Is a man walking to the loo in the back of an airplane moving backwards? How about this one: some amplifiers have sufficient negative feedback so that one could put a signal one the output and measure it on the input. |
#17
Posted to rec.audio.pro
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What is "reverse gain"
"Tim Perry" wrote in
message Incidentally, did you know that 'log' and 'anti-log' controls are named the wrong way round w.r.t. clockwise rotation ? Think about it. Thinking trigonometrically, potentiometers are really exponential, which is the same as the anti-log. How about this one: some amplifiers have sufficient negative feedback so that one could put a signal one the output and measure it on the input. That speaks to a lack of isolation of the input from the output. We expect that in audio amps, just like we don't expect impedance matching. If you think of an amp in terms of an impedance matrix, we expect that the element that describes the influence of the output on the input, is infinite. If as an admittance matrix, then zero. |
#18
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What is "reverse gain"
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#19
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What is "reverse gain"
Tim Perry wrote: Incidentally, did you know that 'log' and 'anti-log' controls are named the wrong way round w.r.t. clockwise rotation ? Think about it. Graham I don't wanna. it hurts my brain. Is a man walking to the loo in the back of an airplane moving backwards? How about this one: some amplifiers have sufficient negative feedback so that one could put a signal one the output and measure it on the input. Possibly you mean insufficient NFB ? Graham |
#20
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What is "reverse gain"
On Fri, 05 Dec 2008 13:46:40 -0800, timewarp2008 wrote:
I've heard of reverse gain as an indicator of gain through a device connected "backwards", i.e. a signal is applied at the output pin of an op amp, and measured at the input pin, gain being measured-at-input divided by applied-at-output. But in the context of pro audio, specifically, microphones connected to mixers in a pro audio (live or recording) situation, what does "reverse gain structure" mean? I plugged an old spring reverb rack in the other day. For some reason, it inverts the phase of the direct signal going through it, and there is no setting that is totally wet. So, when you turn up the reverb aux send on a track, the track gets quieter as the reverb gets louder! It works like a reverse gain control. It's actually quite an intuitive way to use reverb, and there is no sign of modification inside the rack, so I thought it might be wired that way intentionally. |
#21
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What is "reverse gain"
In article ,
wrote: I've heard of reverse gain as an indicator of gain through a device connected "backwards", i.e. a signal is applied at the output pin of an op amp, and measured at the input pin, gain being measured-at-input divided by applied-at-output. But in the context of pro audio, specifically, microphones connected to mixers in a pro audio (live or recording) situation, what does "reverse gain structure" mean? I bet a nickel that it means the _gain structure_ is reversed. That is, reverse modifies structure and not gain. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#22
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What is "reverse gain"
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#23
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What is "reverse gain"
On Dec 6, 5:35*pm, (Scott Dorsey) wrote:
In article , wrote: I've heard of reverse gain as an indicator of gain through a device connected "backwards", i.e. a signal is applied at the output pin of an op amp, and measured at the input pin, gain being measured-at-input divided by applied-at-output. But in the context of pro audio, specifically, microphones connected to mixers in a pro audio (live or recording) situation, what does "reverse gain structure" mean? I bet a nickel that it means the _gain structure_ is reversed. *That is, reverse modifies structure and not gain. --scott So, in this case (hotter microphone output, thus less gain on the input trim), what would be "reversed" about the gain structure? -- "C'est un Nagra. *C'est suisse, et tres, tres precis." |
#24
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What is "reverse gain"
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#25
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What is "reverse gain"
So, in this case (hotter microphone output, thus less gain
on the input trim), what would be "reversed" about the gain structure? Sound in the room is being lowered. No. Compared to other microphones, the electrical signal level is higher at the mixer's XLR input. After the input trim stage, the signal is about the same with either microphone. The sound in the room, both at the microphone, and in the listening area, is the same level with either microphone. Regardless of that, nothing seems "reversed." The gain structure is a bit different in one section of the signal path, but nothing is reversed. It's a tricky thing to do well. Reducing the gain at the input is not tricky at all; it's a simple and straightforward task for anyone famililar with the use of microphones and mixers. All the best fortune, Chris Hornbeck |
#26
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What is "reverse gain"
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#27
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What is "reverse gain"
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#28
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What is "reverse gain"
wrote:
I bet a nickel that it means the _gain structure_ is reversed. =A0That is= , reverse modifies structure and not gain. So, in this case (hotter microphone output, thus less gain on the input trim), what would be "reversed" about the gain structure? Not much. I mean, there's less gain at the front of the chain in order to maintain the same amount of headroom, but it's not as if there is more gain at the other end. I wouldn't call that reversed. In fact, the real system gain structure hasn't changed much, it's just that there is more gain in the mike and less in the preamp. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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