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Wanted: Recording with Real Ultrasonic Content
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Old 23rd April 2020, 04:38 AM   #1
paulfx is offline paulfx  United States
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Default Wanted: Recording with Real Ultrasonic Content

Calling all high-resolution music collectors: What recording can we use as a test for tweeters with an ultrasonic peak? The Peerless DA25TX00-08 and the SEAS E0047-04 T29MF001 have resonant peaks at around 27KHz. Debate rages as to how audible this is at lower ranges:

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Paul FX
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Old 23rd April 2020, 05:24 AM   #2
Douglas Blake is offline Douglas Blake  Canada
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Given that most recordings are brick walled at 22khz you may be forced to resort to a signal generator to get up that high.

But, experience tells me that, first it is unlikely you'll ever hit that resonance and second it is beyond unlikely you'd hear it if you did. This is a full octave above most people's hearing and two octaves above musical content. I wouldn't think it was anything to worry about and certainly not the price of crossover parts to correct it.
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Old 23rd April 2020, 06:11 AM   #3
wiseoldtech is offline wiseoldtech  United States
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Quote:
Originally Posted by Douglas Blake View Post
Given that most recordings are brick walled at 22khz you may be forced to resort to a signal generator to get up that high.

But, experience tells me that, first it is unlikely you'll ever hit that resonance and second it is beyond unlikely you'd hear it if you did. This is a full octave above most people's hearing and two octaves above musical content. I wouldn't think it was anything to worry about and certainly not the price of crossover parts to correct it.



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Old 23rd April 2020, 11:38 AM   #4
Tubelab_com is offline Tubelab_com  United States
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Any digital music storage or delivery system will have a maximum high frequency content equal to or less than half the sampling frequency. This limits a CD to 22.05 KHz in theory, but around 18 Khz in practice. You would need a source recorded and delivered at a minimum of 96 KHz to have any meaningful ultrasonic content.

There was an analog system used for recording 4 discrete channels on a vinyl record that had some popularity in the early 70's called CD4 or CD-4. The two stereo channels are placed onto the record in the usual manner, but the two additional channels were encoded at a higher frequency between 30 and 50 KHz. The records could be played on a conventional turntable for stereo, but a special phono preamp and cartridge was needed for discrete quadraphonic reproduction.

CD4 records were not real popular in the 70's and quite rare today. I had several, but only one left today. The higher frequency stuff gets killed in a conventional phono stage so a custom phono "demodulator" was required for 4 channel outputs. The high end stereo companies made them and they show up at flea markets for cheap. I got a Marantz for $5 once.

I made a simple two channel gain stage to raise the output level to feed an oscilloscope back in the 70's. I used it and a CD4 record to set up turntables. Play record, watch scope and tune up the turntable for the best pair of HF sine waves. You wanted clean signals with matching phase and equal amplitude.

One of the drawbacks of these records was that playing them on a cheap plastic "system" of the day not only destroyed the HF content in the records, it set off any dog in the vicinity due to the HF content mixing with the conventional content in the distortion laden cheap transistor amps of the day.
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Old 23rd April 2020, 03:22 PM   #5
paulfx is offline paulfx  United States
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Maybe I could mix in 27KHz at say, -5db to the average level of the best choral recording I can find? I could check with my cat to see if he reacts to the tone turning on. Verify the level of music is identical in both cases.
And then, and then, enlist my wife to do an A-B test with a momentary switch for the ultrasonic tone to see if she can hear any difference at all.
The nice thing about my wife is she has been in school orchestras and amateur choruses and has a great ear, but she does not care much for SQ. She can hear differences but is happy to listen to her iPhone instead of my system when she has it with her. This would be a single-blind test but she'll tell me what sounds more realistic regardless of my facial expression.
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