Jun 192011
 

From time to time on-line audio tests become available on the web, whereby one can listen to pure sinusoidal test tones, either relayed through one’s audio system or through headphones or speakers plugged into the computer.

These sort of tests are always a bit of a minefield: either you want to know, for good or bad, how well your high frequency hearing is being maintained, or perhaps knowing that you spent much of your misspent youth attending very loud rock concerts, simply don’t want to know by how much your hearing has been damaged. Then there are those who regard these demonstrations as a challenge and either as a face-saving exercise when in denial or simply as an excuse to brag, will often report results that are unlikely given their age.

Even so I recently tried such a test and found I could easily hear a 12kHz tone but none 14kHz or higher. Given that I’m 61, and like it or not, one starts to progressively loose high frequency hearing somewhere between age 40 and 50, I should have been content (if not especially pleased) with that result. But no, I put it down to the poor fidelity of the headphones I was using – the sort that are handed out on planes for the in-flight entertainment.

So I padded over to my system and put the Hi Fi News & Record Review Test Disc (HFN 003) into the CD player and ‘listened’ to tracks 33 through to 36: spot frequencies at 10, 16, 18 and 20kHz. Now these tones are recorded at a very high level (0dB ref. 2V), but to no avail: the 10kHz tone was loud and obvious but the rest silence apart from a low level buzz (these high level high frequencies seem to have upset the Quad 405-2 I was using); the persistency of which was such that it remained when the preamp was switched to another source and could only be eliminated by switching the power amp off and then on again!

Be warned: Do not listen to high amplitude test tones through headphones – there is a great temptation to turn up the volume if you are having difficulty hearing a tone. Even though you are having difficulty hearing the tone, continued exposure at high level is not good for your hearing. If you have any doubts have your hearing tested by a fully qualified audiologist.

So far, so good – or should that be bad? I next pulled out a demonstration record made for JBL Speakers to help their dealers demonstrate to customers what they ought to be listening for. (The record is called “Sessions”, there is no record number but it was recorded by Capitol in 1973. I bought my copy in 1980.) No, it’s not a blatant piece of marketing propaganda but actually a very useful demonstration disc. Not surprisingly it contains a range of test tones with the intention of demonstrating what useful frequency response you need. In doing so I found my electrostatic speakers reproduced the lowest note on a string bass (42Hz) with excellent fidelity. But we are talking high frequencies here and the record has a downward sweeping tone from 20kHz to 10kHz. This time I could hear no better, though I fancied I could just make out tones up to 13kHz.

Now there are some people who recognise they have hearing problems, such as tinnitus and/or high frequency loss and might wonder as a result if they need a full range system. They would not unreasonably ask: “If I cannot hear above (say) 12kHz, why do I need a system that has a response up to 20kHz and beyond?” My reply would be: “Yes you do, for reasons that I will now explain”. Unless you listen exclusively to either pipe organ or to synthesisers, all musical instruments have their fundamentals lying between 38Hz (the lowest note on a contra-bassoon) at one end and 4.698kHz (the top note of a piccolo) at the other. Now there are pitch less instruments that do not have a natural pitch, their pitch depends on how they are played: drums (excepting tympani); cymbals and triangle, but only snare drums and the metallophones have a response going beyond 4kHz. Yet it is the presence of harmonics, the overtones that give instruments their timbre, and these overtones can extend beyond 15kHz.

So we seem to have a dichotomy here. There are some of us who recognise we have age-related hearing loss (presbycusis) yet need to be able ‘hear’ high frequency harmonics so as to give instruments their character. Well don’t worry – you still need a system with an extended high frequency response and even though you cannot directly hear high frequency tones, you will perceive them as harmonics. Returning to the JBL demonstration record “Sessions” [¹], there is a very useful and interesting track consisting of a solo violin with the intention of demonstrating attack and the start of the notes. This track is repeated three times, but at a point roughly halfway through each track, all frequencies above 15kHz, then 12kHz and in the third, 10kHz are filtered out. Now as I have said, I cannot hear direct tones higher than 12kHz, yet the sense of attack and ‘air’ of the violin as the higher frequencies are filtered out is obvious and immediate. It can be heard at 15kHz and is quite obvious at 12kHz – even more so at 10kHz!

It also explains why some audio enthusiasts fit super tweeters to their speaker systems. These super tweeters don’t even start to respond until 20kHz or higher, yet their unstrained reproduction of the subtle harmonics and overtones alluded-to, help accurately portray the timbre of the instruments played. All the more curious: since on vinyl at least, there is virtually no information content above 15kHz.

So even though you might not be able to hear a pure note above, say, 10kHz, you will most certainly perceive the presence of harmonics at frequencies higher than this and you still need a system that can reproduces these frequencies.

One final point – some might have tested their own high frequency hearing and found that there is not necessarily a monotonic roll-off with frequency. Again don’t worry. For years through my late forties and early fifties my hearing started to fall off around 14 -15kHz, with total silence at 16 and 17kHz only to find it returned at 18kHz and then promptly fell away again. Before then I could hear up to 17kHz, then it fell off after that, complete silence at 18kHz only for it to return so I could hear 20kHz! I blame it on a certain very loud Nine Below Zero concert I attended in my mid thirties.

[1] This record (a double LP) is no longer in print, but downloads are available:

Record 1
This is mainly a dissection of the sounds of various instruments and how to recognise the correct tonality. The songs at the the end of side one are also good; not just in sound reproduction but even more so in the musicality.

Side 1: http://www.mediafire.com/download.php?nwzm1m1mtyi
Side 2: http://www.mediafire.com/?mntl5motljm

Record 2
The second record goes deeper into explaining the actual recording process as opposed to the reproduction process. It goes into length about the actual recording session and 16-track recording. It’s amusing to listen to the exchange between the sound engineers and the musicians (Hoyt Axton and friends) from a session over forty years ago.

Side 1: http://www.mediafire.com/?yiyqrlemtn5
Side 2: http://www.mediafire.com/?eno2jvyw2zi

Overall a useful and interesting ‘test’ disc, despite the occasional uncious tone of the narrator.

Barry Hunt

Equipment used:

CD Player, Sony CDP XB-720E

Pre-amplifier, Mark Levinson ML28, using balanced input and output connections.

Power amplifier, Quad 405-2, lightly modified.

Speakers, Quad Electrostatic (‘57s)

© Text Copyright 2011 Barry Hunt

NB No part or portion of this article may be reproduced or quoted without written permission.

 Posted by at 9:54 am

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