How much THD is audible?

August 6, 2021
 by Paul McGowan

20 comments on “How much THD is audible?”

  1. THD is a measurement method that quantifies the severity of non-linear distortion in a signal processing stage, by injecting a pure sine wave test stimulus and measuring the generation of harmonics. We wouldn’t normally be listening to THD, except in the unusual case of feeding a pure sine wave to the amplifier and listening to the output. Not the most riveting listen, but I’m sure that some researchers have investigated the ability of listeners to detect distortion of a sine wave test signal.

    I guess the question is rather: What THD performance should I be looking for in an amplifier to be sure that I’m not going to hear distortion when I use that amplifier to play music. We don’t know for sure how much distortion the amplifier is going to generate given the complex music signal, and we don’t have an accepted measurement method to quantify it.

  2. Good Topic.
    I was just discussing my audio sales experience with Joel at Upscale audio, and relating my experiences in one location where we had quite a stream of Boeing engineers shopping during the day. They were armed with spec sheets and reviews, and would take a salesperson’s time as long as you wanted to discuss the technical.
    A good listen to a great product was the only answer for folks that were technically educated.
    As I matured in that sales environment, I learned how to relate to specs, but steer the session to listening.

  3. I suspect that in the early days of transistor amplifiers manufacturers would quote THD for an output signal just below clipping. This measurement minimises the effect of cross-over distortion. A listener using the amplifier at more realistic levels might experience quite severe and objectional crossover problems. This disappointment can avoided quite easily by measuring THD at 100 mW, 1 W, 10 W, 100 W.

      1. LaszloPhoto,
        As an example, the hardcopy ‘Owner’s Manual’ of my previous 80watt/ch
        integrated included a THD(y) vs Watts(x) graph showing THD at 0.05%
        around 1watt & dropping (sloping) down to 0.006% at 78watts, then
        when it hits 83watts it shoots, & I mean SHOOTS, right up to 10% THD.

          1. An Onkyo – ‘A9070’ believe it or not.
            Bear in mind that this THD figure is what is
            claimed by the manufacturer; not as tested.
            Check page 43 of the ‘A9070’ (pdf) Instruction Manual.

  4. “I believe that second harmonic distortion is sonic gold for audiophiles”
    “… three dimensional and beautiful reproduction of ambience and depth.”

    Stereophile Katz’s Corner 25.
    Bob used a valve to inject measured amounts of 2HD. With only positive listening results. (BHK knew this and Paul was convinced)

    1. Some people (me included) will think that the purpose of an audiophile amplifier is to be as transparent as possible. I don’t think Paul has ever said that the purpose of the valve in the BHK is to deliberately generate distortion.

      1. Reading Katz’s explorations (you seem not to have) his transparency is absolutely retained. With additional unexpected benefits.

        Let me guess that digital dither is a parallel to adding 2hd.

        We used to say “go figure” when explanations seemed elusive.

        1. I have read Bob Katz’s article, but it doesn’t change my point of view; some people will think that a transparent amplifier should add nothing at all to the music. Others will prefer the sound of an amplifier with added distortion. Neither is wrong, and we’re able to spend our hard-earned cash on whatever we want.

  5. I bought a Technics sug 700 integrated amp used (3m old) for a song $1600 a year ago, it drives my canton 9k stand mounter speakers 87dB. I like resolution and man can I hear very good detail, imaging, soundstage all sound great as well to my very old ears. Other than ever so slight thinness inherent to class D amps but largely absent in the sug700 the music is detailed but not harsh or forward sounding. I have Focal elegiac headphones and the resolution of my speakers is almost as good in presenting details guitar string decay violin bow sound over strings that stuff. However, their manual does not say squat about THD+N.nada, zip, zero nor does it contain little useful information. other than 70 watts aside.
    Here is the rub Technics and their parent company Panasonic sucks the hairy wazoo when it comes to customer support. Technic’s manual gives you phone numbers and email addresses all but one phone was working and it was a recording referring me to one of the 4 nonworking email addresses. I called Panasonic much the same. Listen to me now and hear me later avoid these companies like the COVID. Can’t say I don’t enjoy the sound, and feature set ( though missing balanced inputs), and stunning looks but I would appreciate having information about the product. The manual just blows smoke up your patoot listing all their latest tech( which is nothing to sneeze at) My guess is THD must suck since they don’t list it. Did I use enough cliches?

    1. Good morning Scottso!
      Some 34 years ago, I interred in to a sweepstakes that Coke Akola was doing back then.
      The two things that they had up for grabs, was a 1987 GMC Geep Rangler, and a Panasonic stereo rack system.
      I won the sweepstakes.
      But when it came time for me to collect my prizes, they didn’t have any Panasonic stereo systems.
      I got the Geep, but I ended up with a Technics stereo system.
      The THD on that power amp was so high, that I couldn’t stand to turn the volume up on that system.
      I think it was above 2%.
      But when I tested it later, I discovered that, the distortion was coming from the preamp instead of the power amp.
      So ya, I agree with you about that company.

      1. Hi John thanks for the comment. Go figure you put out a number of new products then don’t support them or for that matter get them to reviewers. If you call PS Audio staff they bend over backwards to help same with Emotiva.

        1. Good afternoon Scottso!
          I don’t own any PS Audio products as of yet, but I have spoken to some of the staf members there.
          They seem to be both friendly and knaallageable.
          I’m still holding out for a Sprout.
          But when they ramp up production, I’ll get one of them in my hands.
          I’ve heard of Emotiva, but I have no experience with any of their products.

          1. I by my gear used and have had good success getting gear for half of the cost of new. I mean it blows my mind how much some folks have to spend on this hobby. If you don’t know these sites check out usaudiomart and audiogon. The people on audiogon are knowledgeable and are very helpful. Many have been into audio all their lives.

    2. Very few manufacturers produce a readable manual. McIntosh does a good job at it! Most others including those written in USA are at best poorly written.
      Recently I called a USA manufacturer due to a manual that was confusing and the tech person clearly stated that he knew of the problems but did it write it. Another tech said he was thankful for the poorly written manual otherwise he would be out of a job !

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