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Amplifier clipping - an epidemic?

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  • Amplifier clipping - an epidemic?

    On several threads we have from time to time touched on the subject of amplifier clipping. How serious and commonplace is this issue? I think this is an epidemic problem, and I suspect that amplifier manufacturers are chasing the twin, and dubious, objectives of the illusion of big power at the bottom end of the volume control range (irresponsible, nonsensical comments such as "... this amp punches above its weight") and pandering to the misconception that "small amplifiers sound better". Taken together, amp users are caught-up in the inevitability of their amplifiers running beyond their linear power range for perhaps much or even most of their operating on-time.

    Example threads are here and here, and posts here and here. (to follow)

    I recently created a signal ramp for playback on your PC speakers which increases in loudness until at a critical level - which will to some extent depend upon your equipment - a change in tonality is evident, and the sound becomes 'harder' as unwanted harmonics creep in. Here is that clip again:

    In my opinion, you make a classic description of a small amplifier with a high sensitivity input driven into clipping, which generates hard, harsh harmonics. I've taken a break from playing with my one year old granddaughter (exhausting isn't it!) and I've made an example of the fine line between loud and clipping inside the amplifier. As you can hear, there are six steps in loudness. Steps 1-4 should (on your pc speakers if you are not playing then too loud) sound clean. Steps 5 and 6 simulate a loud CD over-driving the amplifiers maximum output power potential, and the consequence is that spurious tones are generated (in the amp) and sent to the speakers.

    Because the dynamic range of CD is so huge, it makes no sense to me whatever to deliberately choose a small amplifier. It's the most stupid decison that a serious music listener can make, because you need every drop of amplifier power to even begin to approximate to the dynamic range of real music.

    Loading the player ...
    Clipping Clip 1

    On music, the effect is less obvious, but clipped music is fatiguing to listen to because there are no shades of light and dark (it's all light), and the spurious tones generate a sonic glare. Example here, centre section deliberately clipped.

    Loading the player ...
    Clipping Clip 2
    Once clipped, the audio is destroyed. You could spend millions on your system trying to recover that lost natural sound, but you cannot unclip what is clipped.
    It occurred to me overnight that the information I have presented above that the CD player is the primary culprit is far from the whole picture. For example, when I was generating the audio clips for the thread on vinyl v. CD, I discovered after spending an entire evening capturing signals from various test records that somewhere between the the phono input and the tape outputof the QUAD 44 preamp I was using, even when the gain was set correctly to match the pickup cartridge, was clipping and that clipped audio was then fed via the tape output socket to the PC soundcard and also as a clipped signal to the volume control and on to the power amplifier. I had to re-record the entire session using an external, inexpensive, NAD phono amp which had far more headroom and did not clip.

    CD players normally produce 2 volts output for a fully modulated CD; some players even more. 2 volts a/c equates to over six volts peak to peak. If any part of your amplifier - regardless of where it is in the circuit - cannot handle and amplify that huge signal then that is the pinch-point for clipping. And once clipped, it doesn't matter how the volume control is set: the audio is ruined.

    So, our challenge for 2104: let's be sure that our amplifiers are not clipping and if they are not, let's identify the ones that are designed to perform in the real world. How can we identify for ourselves, in our own homes, if our amplifier is linear when driven from a CD player or not?

    Is it clear what happens when an amplifier is driven into clipping and why? Is this clipping issue as common as I fear it to be? Is it self-evident that once an apl is clipping, the sound becomes hard and this leads the hapless listener along a long, expensive and fruitless journey through the land of tweaks and accessories to try and recover the clip-free linear sound they seek?

    Any suggestions as to how we could do a kitchen-table test without equipment seeking the tell-tale signs of clipping?
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  • #2
    A walk-trough about the meaning of 'clipping'

    To be absolutely sure we are not bandying around a technical word like clipping without a decent understanding of what that's pointing to, I'm going to make a little video talk-through of the basics, so we can see and hear for ourselves this phenomena called clipping.

    Just as I was setting up to make the screen cam, my granddaughter crawled in. She was one year old two weeks ago. Her father, our eldest son, had a camera handy and captured for posterity her first exposure to both a desktop PC and audio tones. Just to preserve 'this was the event that changed her life' (some hope!) here is that moment ....

    Loading the player ...


    And now to the talk through itself ... (paying attention Jessica?)...

    To follow (need to make it first)
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

    Comment


    • #3
      'Clipping' - walkthrough #1

      Here is a brief introduction to the subject of waveform clipping. It doesn't matter whether the clipping occurs in the speakers, the pickup cartridge, the amplifier, CD player, tape recorder, transmission chain or in a digital audio file; the effect is the same - the peaks and troughs of the audio waveform are scythed-off. A clipped waveform is the most avoidable and ugliest audio distortion that can effect a recording and/or reproduction system. I hope this opens the subject up a little.

      Remember: clipping is the consequence of trying to ram too loud a signal into a system that cannot cope with it. The horrible audio consequences are avoidable. You simply have to make sure that every element along the audio chain is truly capable of accepting the wide dynamic range (a.k.a. voltage range) of each preceding component, especially that your hifi amp is truly capable of handling the very high voltage (because wide dynamic range) signal from the output of your CD player or digital streaming box.

      It's important to appreciate that avoidance of clipping may have little or nothing to do with the operation of your volume control because the volume control is usually located amongst the output circuitry of an amp/ preamp, not at the input stage. Thus, if the input stages are driven into clipping, it doesn't matter how low you turn the master volume control: the audio delivered to the volume control and onwards to the speakers will already have been clipped.

      Loading the player ...
      Alan A. Shaw
      Designer, owner
      Harbeth Audio UK

      Comment


      • #4
        The sound of .... the trumpet (a brass instrument)

        The next thing I wanted to touch on is the matter of why a piano playing the same melody as a trumpet sound so different from each other. You could not confuse the sonic signature of the piano and the trumpet, could you.

        Here is a solo trumpet:

        Loading the player ...
        Brass 1
        What do you think we'd see if we inspected the sonic spectrum from such an instrument?
        Alan A. Shaw
        Designer, owner
        Harbeth Audio UK

        Comment


        • #5
          Thanks!

          Very clear explanation of clipping there Alan, thanks for that (and for sharing a precious moment with your granddaughter!). Looking forward to part 2.

          Comment


          • #6
            More on the trumpet ....

            Originally posted by broadsword View Post
            Very clear explanation of clipping there Alan, thanks for that (and for sharing a precious moment with your granddaughter!). Looking forward to part 2.
            My pleasure! I'm so pleased that we are able to use technology to bring to life the mysterious world of sound, retaining full control (and copyright) right here on the HUG page. More to come in 2014.

            OK, now listen to this clip, again of a trumpet playing three different notes:

            Loading the player ...
            Brass 2

            How would you describe that sound? Rather harsh? Uncomfortable? Hard on the ear? Not the sort of sound you'd pay to hear unaccompanied? Perhaps you'd say that the sound is rather reedy especially on the highest note?
            Alan A. Shaw
            Designer, owner
            Harbeth Audio UK

            Comment


            • #7
              And now, how about the violin?

              Now how about if we hear similar notes played on the violin?

              Loading the player ...
              Violin 1

              and together, trumpet then violin:

              Loading the player ...
              Trumpet Violin 2

              The tonality is completely different isn't it, especially in the lower note. The violin that so much more mellow sounding, without the edginess of the trumpet. Also interesting to hear how long the body-sound of the violin lingers after the note is bowed, actually for nearly a second. The trumpet, unlike the violin, doesn't have a resonant cavity - the wooden body - to store energy, so almost the instant the player ceases to push energy into the trumpet, the note immediately ceases.

              These two instruments can, as we know, play very beautifully together, so that must mean that they can be tuned to the same fundamental note as each other. In that case, why do they sound so very different? What is it that's added to the basic pitch in the brass instrument that gives it that sharp, incisive, attention-grabbing edge, but is missing or much reduced in intensity in the stringed instrument?

              It's something to do with their harmonic output.
              Alan A. Shaw
              Designer, owner
              Harbeth Audio UK

              Comment


              • #8
                I'm piqued!

                Very informative stuff Alan, piquing my interest in science with music again!
                Many thanks

                I think I'll go read up on harmonics a bit now.
                R

                Comment


                • #9
                  Memories ....

                  Magic moments to be treasured.

                  Comment


                  • #10
                    Detecting clipping - practical example

                    Thanks Alan for these revealing examples. The clipping was clearly audible even on the Tivoli radio two that my wife uses for computer audio. This new knowledge came in useful almost immediately afterwards.

                    I was installing a new flatscreen tv for my fifteen year old son, and connecting it to an external dac (Fiio Taishan with coax input) and an old 70's reciever and some budget speakers that I still had lying around. I had also connected his Playstation 3 to the TV (via the HDMI input) and used that as a BD player. I played Polanski's the Pianist because it is such a well recorded movie. The piano playing in the opening scene sounded harsh. I reduced the output of the tv, and upped the volume on the receiver to achieve the same sound level in the room. The harshness disappeared completely.

                    Just as in your sample, there was a very precise output level on the tv where this change occurred. I am not sure if clipping can occur in a DAC, or if the input stage of the receiver could not cope. So I now need to do the same with the output from his laptop/Behringer usb dac into the same reciever.

                    It obviously also set me thinking about the Quad 33-303 in my main system. Until recently I always played cd's through an attenuator cable, but when I recently had the amplifier combo rebuilt with many new parts the ex Dutch importer service engineer not only changed all capacitors and resistors, but also changed some values to better cope with modern sources. I am not sure what he did precisely (I should have asked) but the amplifier sounded more 'dynamic' (whatever the meaning of such words - but he did show me the better graphs on the scope). It could be the larger and better capacitors in the power amplifier, but I may also have seen and heard less clipping because the input sensitivities were better matched to cd output.

                    That leaves the question if there are easy tests to decide if one's own system is clipping, and where in the system this is occurring. Not all situations are as easy as reducing the output of my son's tv.

                    Thanks Alan for your educating examples.
                    Willlem

                    Comment


                    • #11
                      no clipping after all.

                      Embarrassingly, as my 15 year son cheerfully pointed out, I got it wrong. I thought the tv's inbuilt speakers had been turned off, but that was not so. Therefore, what I heard when I turned up the volume on the remote was simply the tv's tinny inbuilt speakers overshadowing the much better external speakers. Still, the question remains how we can detect/isolate clipping in our systems. Willem

                      Comment


                      • #12
                        An eye opener

                        While post #2 was much cuter, post #3 was more informative than every amplifier review I've ever read. Thanks for that, Alan!

                        I'm looking forward to the answers to this:

                        In that case, why do they sound so very different? What is it that's added to the basic pitch in the brass instrument that gives it that sharp, incisive, attention-grabbing edge, but is missing or much reduced in intensity in the stringed instrument?

                        It's something to do with their harmonic output.

                        Comment


                        • #13
                          How much power?

                          Happy New Year all,
                          below is a neat test to find just how much power is required to drive your speakers to your normal listening levels
                          You may be surprised, I was.
                          http://www.diyaudio.com/forums/multi...kers-need.html
                          It took 11 pages of confusion for some of the guys to "get it", so go to page 11 for the best math explanation.
                          Have fun.

                          Comment


                          • #14
                            Identifying clipping

                            This thread is a superb resource of information - thank you, Alan.

                            I'm very curious to know how we can identify clipping when listening to music as it might help me to understand what I experienced during some demos of loudspeakers, including HL5s. I was aware of something similar to high frequency sine wave tone right at the threshold of my hearing (probably c. 15-16kHz), at very low level but 'overlaying' the music. The sound was not pleasant, as it effected a feeling of physical pressure in the ears (I use a short-hand phrase of 'pencils in the ears' when I hear this kind of sound from speakers). Very fatiguing.

                            Comment


                            • #15
                              CD too hot and subsonics

                              First post on this forum.

                              I recently changed out my amplifier. System since 1998: Rega planet CD/Linn axis TT, Naim Nait 3, Rega jura.

                              Everything sounded ok on vinyl, recording dependent but...and a big BUT, on CD it was a different story. Back in '98 I demoed the CD based system with some nicely recorded quiet (by chance, I just liked the music) CD's and it sounded great. Within a year or so I realized there was a big issue, CD's on average sounded awfully loud through my system. Most CD's went from zero volume to a fatiguing 'loud' at 9 o clock on the amp, I assumed this was technically a type of clipping and by 2002 I'd bought an attenuating cable (-14dB) to help the issue, I simply was not ready to change my amp at that time, I didn't have the funds or inclination so I went with that tweak, anyway the attenuating cable worked well enough, it made the sound much less harsh but it did make the music somewhat uninvolving at the same time.....roll on 12 years of listening mainly to vinyl and I need a change.

                              As you may gather I'm not the person who switches out equipment quickly but enough was enough. I figured that the 75mv! input sensitivity as specified on the naim was probably causing the problem in the first place (clipping at the input with hot cd's??)

                              I did buy a new amplifier that has without doubt helped with the overload? going into the amp, the Rogue sphinx has a quoted input sensitivity of 1Volt and CD is much quieter and I find much easier to listen to as a consequence. Cd's that were unbearable previously (coldplay's parachutes for eg.) are now manageable even if still a bit 'hot'. On average now I will play vinyl or CD!

                              I am kicking myself a bit however as I had recently promised myself two things: that a new amplifier would have tone controls, a subsonic filter and maybe some type of gain trim.

                              I have a second system comprising a basic DJ mixer with gain trim and basic EQ, a crown power amplifier with very flexible EQ, I find the gain control invaluable and the EQ at the amp provides a significant solution to subsonic noise caused by warped vinyl, a fairly coarse high pass filter at 30 Hz significantly eliminates any excess bass cone excursion which I have always found an issue in my regular system (to demonstrate, when you place the needle on the record at high volume setting the cones stay still, without the filter they will bolt out alarmingly by comparison) , on my regular hi fi a very warped record with a low signal is impossible to play at decent volume as the cone excursion can become extremely problematic. (BTW this is not TT isolation, this is due to warped records bouncing the needle around in the cartridge)

                              I have seen very few hi fi amplifiers carry all these features but the NAD 165BEE/275 BEE pre power combo have the all in some capacity: a 10Hz subsonic filter, tone controls and a gain control, at both the pre and power amp section.

                              The extra power (100W at 8, 200 at 4) of my rogue sphinx is allowing the rega juras to play a bit louder generally If needed and the fact that CD's are once again good to listen to is a colossal relief and worth the change so far, but I do wonder if the gain trim/tone controls of the NAD will be useful in the long run.

                              I feel my goal with my system is to make the majority of my recordings at least listenable, I am moving the Juras into my TV room soon and thus am looking for new speakers for the main hifi set up, Harbeth are on the list hence my joining of the forum. I guess my main objectives now are to decide if I should change my amplifier for one with the real world features I like and find really affect the listening pleasure and then audition speaker, including harbeths to find a non fatiguing sound as far as possible.

                              BTW If I want to play very loud and proud I can run the mixer and crown amplifier through my Cerwin Vegas! A pair of harbeths with a decent hifi amplifier should satisfy my more critical listening!

                              Does anybody have experience of the NAD amplifier and can comment on the merits of its tone control, gain control or even the subsonic filter?

                              Thanks in advance.
                              Getting to know my C7ES3

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