Advice on clipping - AVS Forum
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post #1 of 21 Old 03-16-2013, 11:32 PM - Thread Starter
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I'd appreciate some advice about the incredibly unpleasant high end I've been hearing from my system lately. I have an Oppo BDP-105 that I'm running from the multichannel outs directly into my Primare A30.5 amp. My mains are B&W 804s, and the center is an HTM3s. When watching movies, I've been hearing some nasty high end distortion. It's subtle, but when characters raise their voices, there's some faint "crackle" or fuzz; it doesn't happen when characters are speaking conversationally. Also of note, I've having to run the volume on the Oppo at ~75 to get my preferred volume levels. I enjoy my movies loud, but not earbleed levels.

Is I'm hearing clipping? I realize now that despite having been an audio enthusiast for years, I've never been clear as to what that terms refers to. Also, is this likely an amp problem, or is this something in my player or speakers? It's driving me crazy.

Thanks so much for any input!

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post #2 of 21 Old 03-17-2013, 04:29 PM - Thread Starter
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No thoughts? I'd be really appreciative of any guidance or feedback.

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post #3 of 21 Old 03-17-2013, 05:37 PM
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Sounds like the amp is clipping.
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post #4 of 21 Old 03-17-2013, 07:44 PM - Thread Starter
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Quote:
Originally Posted by wronganswerΒ View Post

Sounds like the amp is clipping.

Thanks. Any advice on what might be causing that? Am I just pushing the amp to volume levels beyond its power capabilities?

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post #5 of 21 Old 03-17-2013, 07:59 PM
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Basic issue is the Oppo should be running into a pre-amp/controller then outputted to the power amplifiers.
Even though the Oppo's 2V line-level output will drive a power amplifier, you lack the fine control over its output level which is available when run through a preamp/controller. As now connected it very EZ to drive the power amplifiers into distortion..


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post #6 of 21 Old 03-17-2013, 08:38 PM - Thread Starter
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Quote:
Originally Posted by M CodeΒ View Post

Basic issue is the Oppo should be running into a pre-amp/controller then outputted to the power amplifiers.
Even though the Oppo's 2V line-level output will drive a power amplifier, you lack the fine control over its output level which is available when run through a preamp/controller. As now connected it very EZ to drive the power amplifiers into distortion..


Just my $0.02... πŸ˜ƒπŸ‘

Ah, gotcha. I was wondering if it might be a problem with running the OPPO right into the amp. I'll throw my Krell Showcase back into the chain and see if that helps.

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post #7 of 21 Old 03-17-2013, 09:18 PM
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If you have another amp, check if the speakers dont make strange sounds like the crackle you heard. To me it sounds like the voice coils are bent, making contact with the magnetic motor, and making the sound you described. It happened to my old KLH 's.
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post #8 of 21 Old 03-17-2013, 09:49 PM - Thread Starter
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Quote:
Originally Posted by wronganswerΒ View Post

If you have another amp, check if the speakers dont make strange sounds like the crackle you heard. To me it sounds like the voice coils are bent, making contact with the magnetic motor, and making the sound you described. It happened to my old KLH 's.

Groan. I would be really happy if this is purely an amp question, because I wanted to replace it anyway. Luckily, I've got a good B&W dealer two miles from my house, so I can just haul the 804s in there for a checkup if necessary.

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post #9 of 21 Old 03-17-2013, 09:54 PM
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I'm in the process of setting up a similar system and my reading tells me that the input impedance for directly connecting amps to the oppo 105 should be 47k ohms. Your primare is 10k ohms. If you went the opposite direction and used an amp with an input impedance of 100k ohms, the sound level would most likely be too low when using digital volume control of oppo 105.
47k ohm input impedance seems to be the sweetspot for a directly connected amp.
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post #10 of 21 Old 03-17-2013, 09:56 PM
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Make sure they test them at loud volume. Good luck
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post #11 of 21 Old 03-17-2013, 10:14 PM - Thread Starter
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I'm gonna borrow my friend's Rotel AVR tomorrow and see what happens. Hopefully, it's just the amp and I'll replace it immediately. I'll probably have the 804s checked just to be safe and keep my neuroses at bay.

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post #12 of 21 Old 03-18-2013, 04:53 AM
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Thats good
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post #13 of 21 Old 03-18-2013, 09:58 AM
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At post-clipping occurrence, how do you know if speakers were damaged – are they not going to sound the same anymore even when played at moderate level? Or what behavior do I need to watch out for, in the speaker, without having to increase the loudness before clipping hits again.

The reason for asking this is I seem to have this concern when playing thru Airplay in my receiver and reaching louder volume. The source makes it difficult for me to tell if sound is getting strained or distorted, or think it’s just part of the compression.
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post #14 of 21 Old 03-18-2013, 10:18 AM
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Doesvit happen with other sources?
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post #15 of 21 Old 03-18-2013, 10:44 AM
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Quote:
Originally Posted by wronganswerΒ View Post

Doesvit happen with other sources?

I haven't tried any other sources, yet. I have a PS3 available but has some bass issues when playing CDs.
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post #16 of 21 Old 03-18-2013, 10:45 AM
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Quote:
Originally Posted by XimoriΒ View Post

At post-clipping occurrence, how do you know if speakers were damaged – are they not going to sound the same anymore even when played at moderate level? Or what behavior do I need to watch out for, in the speaker, without having to increase the loudness before clipping hits again.

The reason for asking this is I seem to have this concern when playing thru Airplay in my receiver and reaching louder volume. The source makes it difficult for me to tell if sound is getting strained or distorted, or think it’s just part of the compression.

Be advised that streams on AirPlay are likely, highly compressed which includes high distortion rates..
I would recommend to keep the levels on the lower side..
Or else risk possible loudspeaker damage..


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post #17 of 21 Old 03-18-2013, 10:49 AM
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Quote:
Originally Posted by M CodeΒ View Post

Be advised that streams on AirPlay are likely, highly compressed which includes high distortion rates..
I would recommend to keep the levels on the lower side..
Or else risk possible loudspeaker damage..


Just my $0.02... πŸ‘πŸ˜‰

That makes sense - that's the reason I keep it no more than 60 db volume level. But my concern more is how do I know if I'm doing too much damage to the speaker before it clips?
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post #18 of 21 Old 03-18-2013, 11:09 AM
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Quote:
Originally Posted by XimoriΒ View Post

That makes sense - that's the reason I keep it no more than 60 db volume level. But my concern more is how do I know if I'm doing too much damage to the speaker before it clips?
If your amp is clipping, your tweeters will make strange sounds or die. If you are overpowering your speakers you will bent the voice coils because all the movement and heat in the speaker magnetic motor. In this case you will hear a crackle at loud volume coming from the woofers.
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post #19 of 21 Old 03-18-2013, 11:34 AM
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Quote:
Originally Posted by win200Β View Post

No thoughts? I'd be really appreciative of any guidance or feedback.

One of the tell-tale signs of clipping is that it diminishes greatly and proportionately when you turn the volume down in smooth steps.
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post #20 of 21 Old 03-18-2013, 11:38 AM
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I think a test for damage is to get a "single frequency source" (ie. signal generator / cd test disc), a scope, and a microphone. Basically select a frequency, monitor the input (electrical input to the amp) AND output (with the microphone) on the scope. Slowly adjust the volume watching the results. Of course, the microphone must have good spec and able to handle the levels. Further, you want to be careful not to TRY force the system into "overload"... go towards the level that you normally listen to.... further noting that NOT all the frequencies are being presented so the level may be higher than normally and possibly damaging a single element, ie. n this case a tweeter..... "travel with care". Further if you used your oppo and a test disc, you may actually "witness", where the distortion is taking place, ie. at the output of the oppo or at the speaker.
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post #21 of 21 Old 03-18-2013, 03:58 PM
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Quote:
Originally Posted by budwichΒ View Post

I think a test for damage is to get a "single frequency source" (ie. signal generator / cd test disc), a scope, and a microphone. Basically select a frequency, monitor the input (electrical input to the amp) AND output (with the microphone) on the scope. Slowly adjust the volume watching the results. Of course, the microphone must have good spec and able to handle the levels. Further, you want to be careful not to TRY force the system into "overload"... go towards the level that you normally listen to.... further noting that NOT all the frequencies are being presented so the level may be higher than normally and possibly damaging a single element, ie. n this case a tweeter..... "travel with care". Further if you used your oppo and a test disc, you may actually "witness", where the distortion is taking place, ie. at the output of the oppo or at the speaker.

The even more sensitive version of this test involves the use of two high frequency tones, about 4 KHz apart. In my test I I used 14 and 18 KHz. I generated them with software, in my case Audiion, but the signal can be generated with Audaicty (freeware), for example. In audacity, you generate 2 14 KHz tones with a level of 0.5, pan one left, one right, and then generate 2 more 18 KHz tones with a level of 0.5 and pan one left and pan one right. When you Export them as a stereo wave file, you will have a file with a maximum level of 0.0 dB, and no clipping but with 14 and 18 KHz mixed together in each channel. This is a spectral analysis of the resulting tones:




This is a dangerous tone to play on a stereo system because it can be quite powerful and even destroy tweeters but not be all that loud due to its high frequency.

If even slightly clipped, this is the spectral analysis of the resulting tones:



The clipped cross-modulation products is quite a mess and extremely audibly different from the original tones. I picked the difference between the two tones togenerate cross modulation products in a range where the ear is very sensitive - the 2-6 KHz range.
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