Re: [Repeater-Builder] Repeater Audio samples
On Jul 2, 2009, at 9:14 AM, Scott Zimmerman wrote: While I don't have any recordings for you, I can assure you that ALL machines I build have audio responses that sound as close to simplex as possible. When I am finished with a machine, I have a helper in another room talk into the repeater's input while I toggle my receiver between the receiver's input and output frequencies. If they don't sound REALLY close, the machine doesn't leave my shop. Agreed. Just to throw a little more confusion on the fire here... don't underestimate how bad different user's radios sound, though. More than once I've thought wow, something's wrong with the repeater! while listening to some cheap HT user talking on it, hit the reverse button, and found that their rig's signal just sounds THAT bad... -- Nate Duehr, WY0X n...@natetech.com http://facebook.com/denverpilot http://twitter.com/denverpilot
[Repeater-Builder] Repeater Audio samples
Hello, Was Wondering if anyone had a link to a site that had samples of talk thru Repeater traffic that would be considered good quality audio ? Maybe i am expecting too much but any of the ones around here that i have heard seem either Muffled or very Shrill, Listening on the input frequency the Audio seems quite reasonable but the Transmit Audio doesn't sound the same and seems a bit average. I realize that the Audio will vary due to the normal constraints of Radio atmospherics but i was hoping for something that doesn't sound like a very cheap tiny AM broadcast radio I would be really interested in discovering just how good normal Analogue speech can sound when it is being passed through something that is properly setup. Apologies if this has been answered before, i searched but couldn't find anything specific. Any info gratefully received, Cheers,
Re: [Repeater-Builder] Repeater Audio samples
While I don't have any recordings for you, I can assure you that ALL machines I build have audio responses that sound as close to simplex as possible. When I am finished with a machine, I have a helper in another room talk into the repeater's input while I toggle my receiver between the receiver's input and output frequencies. If they don't sound REALLY close, the machine doesn't leave my shop. There are many things that can lead to distortion in a repeater's audio path. Among these are discriminator response, PL filtering, (if used) controller bandwidth and distortion, and exciter frequency response. The most likely causes of audio response issues are the controller and exciter modulator. Since you describe the audio response as either 'tinny' or 'muffled' that tells me that the audio input response of the controller is not configured properly. *Most* controllers can be used with both discriminator audio or de-emphasized audio. This is often jumper selectable, but sometimes component changes are necessary. I will leave it to the reader to do further research on what these two type of audio are, but suffice to say that most controllers expect to see discriminator audio and have on-board de-emphasis circuitry to make the audio response flat again. If the repeater in question has a 'boomy' sound to it, this is likely a sign of too much low-end audio response. The audio is more than likely being de-emphasized twice inside the system. The best and easiest way to fix this is to remove the extra de-emphasis circuitry. This can sometimes be done on the input circuitry of the controller. If it can't be done there, you may have to look at your Rx audio source. It is common practice to those who don't know any better to use audio from the speaker. It's convenient and it squelches when the repeater is not active. This is a BAD idea. Not only is the audio WAYYY to loud from a speaker's output, it's bound to the volume control. If someone is at the repeater site and decides he wants to listen in on a conversation, there goes the audio setting for the repeater!! Speaker audio is a good example of de-emphasized audio. If the repeater audio sounds 'tinny' it has too many high frequency components. In this case, an additional stage of de-emphasis is required. Again, the easiest way to add this is in the controller's audio circuitry. If the audio is 'muffled', it is probably being processed (compressed) too hard. Inside a transmitter there is circuitry that keeps the audio tamed down and in check to avoid overmodulaton and other band things from happening. This circuitry can only do so much. If it is getting hit with an audio source that is WAYYY to loud, it simply slams it to the ground, hence making it sound bad. This is an over-simplification, but more information on audio processing and how to *properly* set it up can be found in the repeater-builder.com site.: http://www.repeater-builder.com/tech-info/audioprocessing.html (This may be a bit over your head)[sorry Jeff] http://www.repeater-builder.com/tech-info/fmtheorydiscussion.html Sounded like a simple enough question didn't it!! Enjoy, Scott Scott Zimmerman Amateur Radio Call N3XCC 474 Barnett Road Boswell, PA 15531 tait700 wrote: Hello, Was Wondering if anyone had a link to a site that had samples of talk thru Repeater traffic that would be considered good quality audio ? Maybe i am expecting too much but any of the ones around here that i have heard seem either Muffled or very Shrill, Listening on the input frequency the Audio seems quite reasonable but the Transmit Audio doesn't sound the same and seems a bit average. I realize that the Audio will vary due to the normal constraints of Radio atmospherics but i was hoping for something that doesn't sound like a very cheap tiny AM broadcast radio I would be really interested in discovering just how good normal Analogue speech can sound when it is being passed through something that is properly setup. Apologies if this has been answered before, i searched but couldn't find anything specific. Any info gratefully received, Cheers, Yahoo! Groups Links No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.375 / Virus Database: 270.13.2/2214 - Release Date: 07/02/09 05:54:00
Re: [Repeater-Builder] Repeater Audio samples
At 03:22 AM 07/02/09, you wrote: Hello, Was Wondering if anyone had a link to a site that had samples of talk thru Repeater traffic that would be considered good quality audio ? Maybe i am expecting too much but any of the ones around here that i have heard seem either Muffled or very Shrill, Listening on the input frequency the Audio seems quite reasonable but the Transmit Audio doesn't sound the same and seems a bit average. I realize that the Audio will vary due to the normal constraints of Radio atmospherics but i was hoping for something that doesn't sound like a very cheap tiny AM broadcast radio I would be really interested in discovering just how good normal Analogue speech can sound when it is being passed through something that is properly setup. Apologies if this has been answered before, i searched but couldn't find anything specific. Any info gratefully received, Cheers, Where is around here ? From what you are saying it sounds like whomever set up the repeater(s) does not understand de-emphasis and pre-emphasis. From the article at http://www.repeater-builder.com/tech-info/flataudio.html ... Another problem that rears its ugly head unless you know the equipment you are working on intimately... If you pick off raw (i.e. not de-emphasized) audio from the receiver discriminator and pipe it into the microphone jack of a transmitter you will end up with an extra level of pre-emphasis (commonly called double pre-emphasis) that will cause the audio to sound very tinny or shrill (take your home hi-fi, tune to a talk radio station, center the bass and the treble controls, note the audio characteristics, then crank the bass control to minimum and the treble to maximum - and mentally double or triple the overall effect). On a true FM transmitter you can sometimes bypass the pre-emphasis network, on a phase modulated transmitter there is no way around it without adding a de-emphasis network in front of it to compensate. This is why many repeater controllers have a built in de-emphasis network that can be jumpered into the circuit or jumpered out as needed. Likewise, picking audio from the receiver after the de-emphasis network (in some receivers that point is after the volume control and the audio muting part of the squelch circuit) and piping it into a true FM transmitter modulator can produce audio with extra amount of de-emphasis (commonly called double de-emphasis) resulting in a very muffled, bassy sound with no high frequencies (same example as above, but crank the bass control to maximum and the treble to minimum - and mentally double or triple the overall effect). Either of the above two situations is instantly recognizable by an experienced ear. Mike WA6ILQ
Re: [Repeater-Builder] Repeater Audio samples
If I remember I will record a net on one of my repeaters and put it on youtube. The repeaters I set up are so natural you can barely tell the repeater audio from the input audio. My current repeater is a Motorola MSF 5000 using it's stock controller and the audio is quite good. I usually retard the repeated audio about 1 tenth of a kc in deviation so there is less chance for clipping which results in muddy audio. WB5OXQ - Original Message - From: Mike Morris WA6ILQ To: Repeater-Builder@yahoogroups.com Sent: Thursday, July 02, 2009 10:55 AM Subject: Re: [Repeater-Builder] Repeater Audio samples At 03:22 AM 07/02/09, you wrote: Hello, Was Wondering if anyone had a link to a site that had samples of talk thru Repeater traffic that would be considered good quality audio ? Maybe i am expecting too much but any of the ones around here that i have heard seem either Muffled or very Shrill, Listening on the input frequency the Audio seems quite reasonable but the Transmit Audio doesn't sound the same and seems a bit average. I realize that the Audio will vary due to the normal constraints of Radio atmospherics but i was hoping for something that doesn't sound like a very cheap tiny AM broadcast radio I would be really interested in discovering just how good normal Analogue speech can sound when it is being passed through something that is properly setup. Apologies if this has been answered before, i searched but couldn't find anything specific. Any info gratefully received, Cheers, Where is around here ? From what you are saying it sounds like whomever set up the repeater(s) does not understand de-emphasis and pre-emphasis. From the article at http://www.repeater-builder.com/tech-info/flataudio.html ... Another problem that rears its ugly head unless you know the equipment you are working on intimately... If you pick off raw (i.e. not de-emphasized) audio from the receiver discriminator and pipe it into the microphone jack of a transmitter you will end up with an extra level of pre-emphasis (commonly called double pre-emphasis) that will cause the audio to sound very tinny or shrill (take your home hi-fi, tune to a talk radio station, center the bass and the treble controls, note the audio characteristics, then crank the bass control to minimum and the treble to maximum - and mentally double or triple the overall effect). On a true FM transmitter you can sometimes bypass the pre-emphasis network, on a phase modulated transmitter there is no way around it without adding a de-emphasis network in front of it to compensate. This is why many repeater controllers have a built in de-emphasis network that can be jumpered into the circuit or jumpered out as needed. Likewise, picking audio from the receiver after the de-emphasis network (in some receivers that point is after the volume control and the audio muting part of the squelch circuit) and piping it into a true FM transmitter modulator can produce audio with extra amount of de-emphasis (commonly called double de-emphasis) resulting in a very muffled, bassy sound with no high frequencies (same example as above, but crank the bass control to maximum and the treble to minimum - and mentally double or triple the overall effect). Either of the above two situations is instantly recognizable by an experienced ear. Mike WA6ILQ
