From: jrwalliker@gmail.com   
      
   On 14/11/2025 14:51, Liz Tuddenham wrote:   
   > Jan Panteltje  wrote:   
   >   
   >>> Bill Sloman wrote:   
   >>>> On 13/11/2025 5:02 am, john larkin wrote:   
   >>>> On Wed, 12 Nov 2025 17:28:04 GMT, Jan Panteltje    
   >>>> wrote:   
   >>>>   
   >>>>>> john larkin wrote:   
   >>>>>>> On Wed, 12 Nov 2025 16:11:03 +1100, Bill Sloman    
   >>>>>> wrote:   
   >>>   
   >>>    
   >>>   
   >>>> The problem is to find an audio spectrum analyzer with -150 dB   
   >>>> distortion.   
   >>>   
   >>> Not if you filter out almost all of the fundamental before you feed the   
   >>> residual signal into the spectrum analyser.   
   >>   
   >> In the old days I tested the Eurovision sound connection from otehr   
   countries   
   >> by having them send a 1 kHz tone, and then measured the harmonics   
   >> with a selective voltmeter.   
   >> Some math and you got a distortion value.   
   >>   
   >> Simple.   
   >   
   > Two-tone intermodulation distortion measurement is even easier to use,   
   > the resullts are read directly off a meter. It deserves to be used more   
   > often.   
   >   
      
   It has been used in the human and some animal ears.  A healthy   
   cochlea generates intermodulation products that can be measured   
   using a microphone in the ear canal.  If the cochlea is diseased   
   the intermodulation products go away.  Acoustic time domain   
   reflectometry also works on the ear.   
      
   John   
      
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