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Audio Tests

What is the correct way to do a walk test?

To test receivers under field conditions is a real pain and is rarely done properly, even at Lectro (!) in…

To test receivers under field conditions is a real pain and is rarely done properly, even at Lectro (!) in the past. To do proper receiver tests, all receivers must be on the same frequency, picking up ONE, I repeat ONE (!!!), transmitter and must use the same receive antennas with 2 two way splitters giving each receiver under test exactly the same signal at the same time. This removes transmitter antenna differences, RF interference differences and receiver antenna differences. Comparisons are rarely done this way and therefore always inexact (wrong).

Here are some things that we found that loused up our two transmitter, two receiver comparison tests big time:

  1. Since transmitter antennas are rarely bent the same and therefore are at different distances from the body, the RF from the two transmitters is mismatched.
  2. Since the transmitters are at different places on the body, reflections from objects in the area are aways different.
  3. Since the transmitters are at different frequencies, the two points above are different as well as different RF noise from the environment. Keep in mind, RF that doesn't show up on the receiver's scan function can make large differences in reception when you are trying to receive weak signals, i.e., check range.
  4. If the modulation (gain) of the two transmitters is not set exactly the same, one receiver can seem to have an advantage. This would show up more when comparing different brands.
  5. The antenna placement of the receiver antennas causes just as many problems as the transmitter points made above. After all, the receiver antennas can't be in the same place simultaneously unless you use the splitter method described above.


This says that comparing two brands of receivers, transmitters, etc., is a crap shoot at worst and difficult at best. Of course, after being beaten unconscious by the sales people multiple times, I've learned to keep my mouth shut when a customer tells me how much better our equipment works than brand X. If you still want to compare two different pieces of wireless gear, I recommend multiple walks, switching frequencies multiple times, changing positions of the transmitters and moving the receivers around so that they occupy each others spots on different walks. You must also set the two transmitters up for correct or full modulation and then set the two receivers to have the same audio output level. To get valid results without the splitter setup and single transmitter described above, requires lots of tests and much walking.

Posted 3 months agoby LectroAdmin
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What is the Hardwired A-B Test and what precautions do I need to take?

This test is a matter of setting up two identical microphones, into a mixer, one connected with an audio cable…

This test is a matter of setting up two identical microphones, into a mixer, one connected with an audio cable and the other with a wireless system, to perform a listening test. An even better way to perform the test is to split a single mic signal so that one path is through the wireless mic system to the mixer and the other is hardwired to the mixer. Though seemingly simple, there are several mistakes that can really mess up the results:

  1. The listening levels of both paths must be EXACTLY the same. Even a very slight difference in level will “fool” the ears into hearing differences that may not actually exist.
  2. The test absolutely requires two people. One person speaking and the other person listening. A single person hears the sound coming from their own mouth and the sound coming from the sound system and the sounds combine at their ears to give very misleading results. This particularly true with systems that have audio delays (digital wireless systems or mixers). Even having the two people in the same room is enough to mess up the results. The only way to do the test with one person is to use a very high quality, pre-recorded signal as the source.
  3. Keep in mind that the truer system is not the one that sounds brighter or warmer or bassier but the one that sounds most like the hardwired signal. You'd be surprised how many people ignore this fact.
  4. If you have to use two microphones, it is always a good idea to swap the microphones and listen to them a second time to see if there are slight differences in the microphones themselves that may have been detected in the first comparison.
  5. If you have to use two microphones make sure they are positioned exactly the same from a sound source or someone’s mouth so the the same audio signal enters both microphones.
  6. Slight amounts of background hiss will make the overall sound of that signal seem brighter. It is a known pre-sensitization effect in the ear. Make sure that the gain of the wireless system is set properly so that background hiss is minimized.
  7. If at all possible, use headphones. Again, it's not whether you like the sound it is how close is the wireless system path to the direct wired path. Headphones are much more analytical and make it many times easier to hear small errors in sound reproduction.

Switch back and forth between the cabled and the wireless setup as the listener compares the sound of each setup. This, of course, is best done in a “blindfold” manner where the listener has no way of telling which setup is being monitored, and by writing down a few notes about the results.

Posted 3 months agoby LectroAdmin
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How is the IM transmitter (for the IS400 instrument system) different than the standard LM bodypack transmitter?

The IM has an extended low-frequency response (-3dB at 35Hz vs. -3dB at 70Hz) when compared to the LM bodypack…

The IM has an extended low-frequency response (-3dB at 35Hz vs. -3dB at 70Hz) when compared to the LM bodypack transmitter. Otherwise, they are the same.

Posted 3 months agoby LectroAdmin
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How is the UH400TM transmitter (for test & measurement) different than the standard UH400A plug-on transmitter?

The UH400TM has an extended low-frequency response (-3dB at 35Hz vs. -3dB at 70Hz) when compared to the UH400A. This…

The UH400TM has an extended low-frequency response (-3dB at 35Hz vs. -3dB at 70Hz) when compared to the UH400A. This allows for sound system measurement when testing low frequency system response.

Posted 3 months agoby LectroAdmin
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I know what a walk test is but what is a "Short Range" Walk Test?

A “short range” walk test checks to see how well the receiver handles deep multi-path nulls that occur at a…

A “short range” walk test checks to see how well the receiver handles deep multi-path nulls that occur at a close operating range with a generally strong RF signal. This tests how well the squelch and the diversity system works. This test corresponds well with real world use where the Classic Walk Test is a test of range at distances that are rarely encountered. Do not remove the antennas on the transmitter or receiver to worsen the conditions, as this will negate the validity of the test.

Before conducting these tests, the wireless mic system should be set up exactly the way it will be used. The microphone and transmitter must be in the exact postition on the talker’s body where they will be used, and the receiver must be connected to whatever equipment it will feed, with power and antennas connected and positioned as in actual use. Unless the wireless system is set up this way, the results of the walk tests will not be realistic. Do not remove antennas on the transmitter or receiver to try to simulate extreme operating range, as this will alter the way some receivers work, such as Lectrosonics models that use SmartSquelchTM and SmartDiversityTM circuitry. 

If you have a frequency selectable system, try the walk test using at least 3 different frequencies since even tiny amounts of interference can radically change the results. If you are comparing two systems, try to select identical frequencies of operation thereby comparing apples to apples. If the receivers have scanning functions, check test frequencies that are free of interference As little as 1 uV of interference can reduce a good systems range by one half.

Find a location where multi-path reflections will be abundant, such as an area with lots of metal file cabinets or lockers, a medium to small metal building, a metal trailer, etc. Place the receiver antenna/s within a couple of feet or so of a metal surface to exaggerate multi-path cancellations at the antenna. The antennas on a diversity receiver need to be at least a 1/2 wavelength apart to achieve the maximum benefit of the diversity technique. If the receiver cannot be configured this way in actual use, then position the antennas as they will be used.

Walk around the area with the transmitter while speaking and try to find a location where a dropout or squelch (audio mute) occurs. Moving the transmitter around within a couple feet of a metal surface may help to generate a multi-path condition. The idea in this test is to see how prone the system is to producing dropouts, and to look for loud noise bursts that occur during a dropout if and when one does occur. An effective diversity system will make it difficult to find a dropout, which will tell you something about the effectiveness of the diversity circuitry. 

If and when a dropout does occur with a strong average RF level at the receiver, the receiver should simply mute the audio during the dropout and not allow any noise or noise burst to occur. An aggressive squelch system in the receiver is best in a close range situation, as it will eliminate noise bursts created by dropouts, however, it will also limit the maximum operating range as in the previous test. A less aggressive squelch allows maximum operating range, but will generally allow noise bursts to occur during dropouts at close range.

The two walk tests "Classic" and "Short Range" illustrate the dilemma of a conventional squelch system in having to choose between either close range or distant operating range, and also illustrates the benefit of an adaptive squelch system like the Lectrosonics SmartSquelchTM which automatically configures itself for close range or long distance operation as the system is being used. The tests are also a good proving ground for Lectrosonics SmartDiversityTM. 

After conducting both types of walk tests, you will have a good idea of what to expect in actual use. Some systems may provide excellent maximum range characteristics, but prove to be noisy in short range, multi-path conditions. Other systems may be great at the short range test, but be poor performers in the maximum range test. Of course, the ideal wireless system would do well in both tests.

Posted 3 months agoby LectroAdmin
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What is the Classic Walk Test?

The classic walk test is to see how far away you can get with the transmitter before dropouts are bad…

The classic walk test is to see how far away you can get with the transmitter before dropouts are bad enough to make the system unusable. You can walk until a count of 8 to 10 dropouts occur, for example, and define that as the limit of the range. Or, walk until the dropouts or hiss buildup is objectionable according to your own assessment. When comparing two or more different wireless systems, it is very important to repeat the same exact path for each walk test, position the receivers and the transmitters on the body in the same location with the same interconnections, and apply the same criteria to define the limit of the range, or it will not be a valid comparison. Even if the maximum range of the system is well beyond what you would normally need, this test will demonstrate the sensitivity of the receiver and how well the system handles weak signal conditions in general.

Before conducting these tests, the wireless mic system should be set up exactly the way it will be used. The microphone and transmitter must be in the exact postition on the talker’s body where they will be used, and the receiver must be connected to whatever equipment it will feed, with power and antennas connected and positioned as in actual use. Unless the wireless system is set up this way, the results of the walk tests will not be realistic. Do not remove antennas on the transmitter or receiver to try to simulate extreme operating range, as this will alter the way some receivers work, such as Lectrosonics models that use SmartSquelchTM and SmartDiversityTM circuitry.

If you have a frequency selectable system, try the walk test using at least 3 different frequencies since even tiny amounts of interference can radically change the results. If you are comparing two systems, try to select identical frequencies of operation thereby comparing apples to apples. If the receivers have scanning functions, check test frequencies that are free of interference As little as 1 uV of interference can reduce a good systems range by one half.

Posted 3 months agoby LectroAdmin
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What is the Input Limiter Test?

In this test, you will need to make some loud noises at the microphone, but be able monitor the output…

In this test, you will need to make some loud noises at the microphone, but be able monitor the output of the receiver in a fairly quiet environment. It’s best done with two people. The purpose of this test is to listen to how well the transmitter input limiter can handle audio peaks well above the average level. 

Set up the wireless system for an average level so that the system indicates brief peaks at full modulation with a normal voice, with the microphone at a distance of 2 feet from the talker’s mouth. While the talker speaks at a constant level, bring the microphone closer and closer to their mouth. Make sure breath pops don’t get into the microphone when it gets close to the mouth by keeping the microphone to the side of their mouth. If the transmitter has a poor limiter, or no limiter at all, the signal will get louder and then begin to distort as the loudness increases. In a system with a good limiter, the sound will get louder up to the beginning of limiting, and then will remain at a fairly level volume even as the mic is moved closer to the mouth. The character of the sound may change due to the different distances as the mic is moved closer to the talker’s mouth, but the system should be able to handle the higher levels without distortion. 

You can also test a limiter by shouting into a microphone, but keep in mind that the character of the talker’s will change as they go from a speaking voice to a shout. This makes this method harder to judge. Some wireless system designs try to prevent overload by having low microphone gain available to the user. This compromise will result in a poor signal to noise ratio when the RF signal gets weak

Posted 3 months agoby LectroAdmin
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What is the low frequency "Bump Test"?

This test will reveal the inherent signal to noise ratio of the wireless system and how well the compandor handles…

This test will reveal the inherent signal to noise ratio of the wireless system and how well the compandor handles low frequency audio signals. The “inherent signal to noise ratio” is the signal to noise ratio before companding. This test requires listening to the system in a very quiet environment with minimal background noise. Place the transmitter and microphone in a different room from the receiver, or use high isolation headphones to monitor the audio output of the receiver. In either case, there must be minimal background noise near the microphone. Background noise at a high enough level will negate the test.

Set up the system for normal voice levels, then place the transmitter and microphone on a table or counter. Make a fist with your hand and gently bump the table with the meaty part of you hand (not your knuckle). The idea is to generate a low level, low frequency “bump” near the microphone at just enough level to open the compandor on the wireless system. Try varying how hard you bump the table with your fist to find a low level that just opens the compandor and listen to the results. When you“bump” the table, listen for background noise that sounds like a “whoosh” or “swish” that accompanies the sound of the bump.

The idea is to listen to how much background noise is released through the wireless system when the “bump” occurs, and also to whether or not the “bump” heard through the wireless sounds the same as in real life.
This is an excellent test of the difference between a single-band compandor and a dual-band compandor with DNR filtering, as well as a test of the signal to noise ratio of the wireless system. With the transmitter gain set for a normal voice level during this test, the results you hear will be what the system will actually do in real use.

It is also interesting, although not a valid test, to set the transmitter gain at minimum, then turn the receiver output up to maximum, and do the bump test again. The only reason to do this is to help understand just how much noise is actually suppressed by the system in normal use, and to emphasize the importance of proper transmitter gain adjustment.

A wireless mic system design that uses a large amount of preemphasis/ de-emphasis as noise reduction will likely do fairly well in the “bump test,” however, it may also fail miserably in the previous “car key test.” (See Dreaded Key Test)

Posted 3 months agoby LectroAdmin
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What is the Dreaded Key Test?

This simple test reveals how well a wireless mic system can handle high frequency audio transients and, in fact, the…

This simple test reveals how well a wireless mic system can handle high frequency audio transients and, in fact, the quality of the entire audio processing chain in the system. Set up the wireless system with a pair of headphones or a sound system at a fairly high level without feedback. It is best to be able to listen to the audio output of the receiver away from the acoustic sound that the keys themselves generate. Set the input gain on the transmitter for a normal level with an average speaking voice.

Gently shake the key ring loosely near the microphone so that the keys jingle and rattle. Shake the keys within a foot or so of the microphone, then move them gradually away from the microphone while you shake them until they are as much as 8 to 10 feet away from the mic. Listen to the audio that comes out of the receiver. Does it sound like car keys, or a bag of potato chips being crushed?
Next, have someone talk into the wireless system while the keys are shaken as in the previous paragraph. Listen for distortion of the talker’s voice while the keys rattle. Move the keys from a foot or so from the microphone and then away from the microphone to as much as 8 to 10 feet and listen to the effect on the talker’s voice.

This is a tough test for anything other than a hard-wired microphone. The results you hear will tell you, without argument, how well the input limiter, and compandor attack and decay times work in the design, and give you a clear idea of the audio quality you can expect from the system in real life. A loosely shaken set of metallic car keys on a key ring produces large quantities of high frequency transients. A wireless system that fails this test miserably, and a lot do, will also distort sibilants in the human voice. Often listeners don’t notice this high frequency transient distortion because sibilants don’t have a specific frequency but are more like random noise. Distorted random noise still sounds like noise. On a system that fails the key test, however, strong sibilants won’t have a clear, open quality but will instead have a muffled sound as if someone’s EVALUATING WIRELESS MICROPHONE SYSTEMS hand has been put between the mouth and the mic. The key test will warn you to listen closely for the effect. The key test will also reveal audio circuits that are upset by supersonics. The peak energy of jangling keys is actually around 30 kHz, well above human hearing. If the circuits in the transmitter don’t filter out the supersonics, the compandor will respond grossly. This is a valid test since sibilants in the human voice also contain supersonics. Supersonic overload will cause sibilants to sound ragged as the level is driven up and down by sounds you can’t hear.

Posted 3 months agoby LectroAdmin
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I, like most wireless users, don't have test equipment. What kind of simple tests can I perform to choose a wireless?

There are quite a few you can do with just your ears and some others that require a minimum of…

There are quite a few you can do with just your ears and some others that require a minimum of audio gear. I'll list some tests you can do, a simple explanation of what that test can show you and then a link to a longer explanation of how to do the test and how to interpret it. The best way to do the tests is simultaneously as a comparison in performance between several systems. It is easy to forget what a given system sounds like if there is a day or so between tests. Sometimes the differences are so dramatic you could remember them years later though.

  1. The Dreaded Key test. Some people complain that this test only shows how well a system reproduces keys. Though true, it also indicates how well a wireless system will handle sibilants. Doing poorly on this test will generally correspond to roughness or spitting in sibilant reproduction. This due to gross overload in the audio circuits due to large amounts of pre-emphasis in the transmitter. Frankly most listeners are not critical of sibilants since if a performer sounds an "s" all they are looking for is a corresponding hiss out the sound system. However, if you are a critical listener, once heard it is hard to ignore. (See Dreaded Key Test)
  2. The Bump Test. This test will reveal the inherent signal to noise ratio of the wireless system and also how well the compandor handles low frequency audio signals. The “inherent signal to noise ratio” is the signal to noise ratio before companding. Poor results in this test will indicate a system that has what is commonly refered to as either "breathing" or a "halo" around the sound. (See Bump Test)
  3. The Input Limiter Test. This test will check to see if the transmitter has an audio input limiter (most don't) and if it does have one, how well the limiter performs. A good limiter lets you operate closer to full modulation, reduces overload distortion and improves the noise and interference performance. Screaming into the microphone is not the best method of checking this feature. (See Input Limiter Test)
  4. The Classic Walk Test. As the name implies, this is a test where one person takes a walk while talking into the transmitter,and the other person listens to the receiver output. The classic walk test is to see how far away you can get with the transmitter before dropouts are bad enough to make the system unusable. You can walk until a count of 8 to 10 dropouts occur, for example, and define that as the limit of the range. Or, walk until the dropouts or hiss buildup is objectionable according to your own assessment. (See Classic Walk Test)
  5. The Short Range Walk Test. A “short range” walk test checks to see how well the receiver handles deep multi-path nulls that occur at a close operating range with a generally strong RF signal. This tests how well the squelch and the diversity system works. This test corresponds well with real world use where the Classic Walk Test is a test of range at distances that are rarely encountered. (See Short Range Walk Test)
  6. The Hard Wired A-B Test. This requires a simple mixer two identical microphones, one connected with an audio cable and the other with a wireless system, to perform a listening test. Better than two mics would be to split one audio or mic signal so that one part goes through the wireless system and the other is direct. (See Hard Wired A-B Test)
Posted 3 months agoby LectroAdmin
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