Deep Dive

    To Test or Not to Test, That is the Question? Part Two

    Issue 126

    In the last installment, I discussed the most quoted test measurement in audio, total harmonic distortion ((THD), and its correlation with sound quality. Once upon a time, audio magazines mostly gave a summary of the features of the equipment under review and the results of laboratory measurements only. J. Gordon Holt, editor and founder of Stereophile magazine was the first to break the mold in giving descriptive accounts of the sound of audio components. The pendulum swung even further in the subsequent years, with many reviewers concerned only about perceived sound quality and paying scant attention to the technical aspect of audio equipment.

    There is a school of thought that opines: if a piece of equipment sounds good, so what if it measures poorly? The problem is that we do not have a standard for comparing subjective evaluations. How wide should the soundstage be? What is the correct tonal balance? Are the dynamics, both macro and micro, reproduced in full? As we do not know what a particular recording should sound like in the first place, it is difficult to know if it is being accurately reproduced by an audio system.

    We can only use audio systems we are familiar with as references. A recording might sound bad in a system because it is how it should sound, whereas another system might mask its faults and make it sound better than it is. That does not mean the second system is “better” than the first. This problem is perhaps more important for recording and mastering engineers than for audiophiles. Engineers want systems that reveal as much as possible, warts and all. Many audiophiles might find such systems difficult to live with.

    To a certain extent, audiophiles can judge the merits of audio systems by comparing with their experience with live music, at least for recordings based on acoustic music. That’s why it is important for dedicated audiophiles to attend concerts and live music events regularly in order to provide a frame of reference. I attend concerts in concert halls, in salons, in jazz clubs and in friends’ homes. During the performances, I often pay attention to the sound as if I were evaluating an audio system, in order to take a mental snapshot of the sound of real musical instruments in a particular acoustic environment for later reference. I also mentally try to work out the best way to record these performances. Lots to think about but part of the fun! Even so, I do find measurements to be helpful in finding weaknesses and faults in a system, which might not be so easy to work out by means of subjective evaluations.

    I enjoy buying audio gadgets as much as any audiophile, and our hobby is full of gadgets; cable lifters, grounding boxes, anti-static guns, LP ionizers, Mpingo discs, tube dampers and a lot more. (I wouldn’t call isolation platforms and record cleaners gadgets, as they are pretty much essential.) In my experience, some of these make a perceptible difference, others don’t. Some are so costly that it is difficult to differentiate between a placebo effect (the more expensive the gadget, the larger the effect) and a real difference.

    What I find the most useful though, and the most fun to use, is test equipment. One can spend a lot of time learning and perfecting the use of these types of equipment, and the result is often highly satisfying. Being an amateur without a professional engineering or acoustics background, I am probably just scratching the surface of what test instruments can offer. Nevertheless, I feel I have already made worthwhile improvements in my listening enjoyment using these gadgets. I would like to share my experience with Copper readers.

    The first gadget I want to talk about measures the most important component of your audio system. No, not the speaker cables; it’s your hearing! I have always been aware of the need to protect my hearing since my high school days. Just before my final piano exam 40 years ago, I decided to clean my ears with Q-tips so that I could hear better during the aural test section. I must have pushed the ear wax further into the ear canal, as one ear became totally blocked. Panicking and running out of time, I went straight to the exam with one ear essentially deaf. I will always remember the anxiety of not being able to hear as well as I should under such circumstances, but I often use this as an excuse for my subpar exam result.

    For years, I carried a pair of foam ear plugs whenever I went to discos, parties and concerts, in case the music got too loud. Aside from exposure to loud noise, there are many pathologies that can cause hearing loss, sometimes gradual, sometimes acute. Gradual hearing loss can be difficult to detect, and it is important to diagnose these problems early, since prompt treatment could preserve function and even reverse hearing loss.

    Hearing tests have been around for decades, and are usually performed by an audiologist in a soundproof booth. I came up with the idea of designing an inexpensive equipment setup for home testing, which would generate a frequency response plot that audiophiles could upload into their DSP equalizer. I approached a colleague who operated a hearing center as someone who could potentially collaborate on this, and he agreed that it was an interesting idea. I surfed the web to see if this had already been done, and lo and behold, someone had already beaten me to it. An Australian ENT doctor had teamed up with an engineer and designed a pair of headphones and an app, which pretty much do the same thing as a professional hearing test.

    They were looking for funding on Kickstarter. I therefore put my money down and waited. It took almost two years before I received the headphones. Called the Audeara A-01, they are nice, generic-looking Bluetooth noise cancelling headphones, but they also have built-in DSP functionality and their frequency response has been calibrated for hearing test purposes. The user needs to download the app and do the test in a quiet room. The test covers the frequency range between 100 Hz and 20 kHz, and comes in three different resolutions. The ultimate test consists of 32 frequency points and takes 10 minutes to complete. A series of beeps are played into one ear, and the user raises or lowers the volume with two on-screen buttons until the sound is barely perceptible. The user then taps another button to record the level and move on to the next frequency. The test starts at 1 kHz, goes up to 20 kHz, then returns to 100 Hz and goes up to 900 Hz to complete the test. The left ear is tested first, and then the right. It is best not to look at the screen while tapping the buttons until you are ready to record the level, as there is a temptation to cheat if one feels one should be able to hear at a certain level!

    The app can change the frequency response profile of the headphones to compensate for the non-linearity of the user’s hearing response. I tried that and found the result sounded rather unnatural.  Although the threshold for hearing high frequencies increases with age (in other words, the high frequencies have to be louder in order to be heard), the brain probably compensates and the perception of loudness is normalized once the level is above the threshold of audibility. For example, if the threshold of hearing a 1 kHz tone is at 30 dB, and the threshold for 10 kHz is at 50 dB, when both tones are played at 70 dB, the brain still perceives both as near-equal in loudness; if you boost the 10 kHz tone to 90 dB, it will sound 20 dB louder than the 1 kHz tone.

    My hearing test, using the Audeara A-01. The two highest frequencies elicited resonances, which I could hear at high volume, hence the uptick at the end. I definitely could not hear those tones!

    People who have high-tone hearing loss (defined as between 2 kHz and 8 kHz) have trouble understanding speech, since they cannot hear the consonants. When their interlocutors speak louder to compensate, they are often rewarded with the admonishment, “You do not have to shout. I can hear you!” This is because once the volume is above the threshold, it immediately sounds loud, as if the volume control goes from 0 to 80 dB in one step. This phenomenon is called recruitment. Even with the gradual decline in high-frequency acuity over the decades, I do not find familiar music sounding duller now than when I heard it in my youth, as long as the music is played at a sufficient volume (to the annoyance of my wife). The DSP function of the Audeara A-01 headphones is probably useful for people with significant high-tone hearing loss (the headphones also have a microphone and can therefore be used for making phone calls), but would not improve the tonal balance of music. Nevertheless, the hearing test function of the headphones is already worth way more than their modest cost, and I find the noise-cancelling function useful when I travel. I go through the test every three to four months, or whenever I feel paranoid.

    The million dollar question is: at what level of hearing loss would someone start to lose the enjoyment of music?  After all, the fundamental of the highest note on a violin is at 3.5 kHz, and that of the piccolo, the highest note of any instrument, is 4 kHz. One does not need to hear above 12 kHz to fully appreciate these instruments, since most of the overtones are second and third order.

    There are anecdotes of elderly conductors who spent their whole career in front of orchestras without using hearing protection, and who need to wear hearing aids to conduct conversations, but nevertheless are able to pick out which violin is playing out of tune with the orchestra when playing tutti.

    During the Hong Kong High End Audio Visual Show last year, I was introduced to a new friend called Wilson. He had just celebrated his 85th birthday, and he was a good friend of the late Arnie Nudell (physicist, loudspeaker designer and co-founder of Infinity Systems and Genesis Technologies). Wilson bought one of the first Genesis 1 loudspeaker systems to roll off the production line, which he is still using. He built a dedicated listening room within the warehouse of his import-export business, where he stores his large collection of professional reel to reel tape machines and master tapes. He goes to the listening room daily to tinker with his toys. Wilson has to wear hearing aids in order to conduct conversations unless the surroundings are very quiet.

    My friend Wilson in his listening room. He got those JBL 4350 loudspeakers recently, and added Altec horns on top! They certainly play loud enough, even for him.

    A group of us visited him at his listening room one Sunday afternoon last fall. His system was very impressive indeed; detailed, with life-like dynamics and an imposing sense of scale. When he told us about the improvements he noticed after installing new cables and tube-rolling his conrad-johnson preamplifier, some of us were rather skeptical; could he really hear the differences, or was he just imagining things?

    A few weeks later, the same group met at my home. I wanted to hear their impression of the differences between my solid state and my DIY tube tape head preamplifiers. Wilson was the first to point out the differences in string tone and the space between instruments while playing Analogue Productions’ The Power of the Orchestra Ultra Tape. He was spot on. It made me feel better that there is life after 60 (or 70, or 80) after all!

    Header image: Audio Precision B Series APx525 audio analyzer.

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