Subsonic Filter

[Confused]

I did consider posting this in the "effects of SAM" thread, but though on balance it deserved a new thread.

Since getting SAM for the KEF Blades, have noticed the very occasional track that sounds a little strange with SAM, or displays some kind of "bass artefact", for want of a better term.  These are very low frequency "puffs" of other not very musical low bass effects.

I had a theory that these seemingly negative effects of SAM could be eliminated by adjusting the speaker positioning.  For  while, if I ever listened to a track that I felt was producing some sort of bass artefact, or if the bass was simply extremely overblown in some way, I placed the subject track into a playlist.  The idea being that when I had a few of these tracks compiled, I could experiment with speaker positioning, to see what effect it would have on these particular tracks.

Today I spent some time trying to tidy up the cabling of my system, and to facilitate this I had moved the speakers.  With this complete, I positioned the speakers a full 10" (250mm) further away from the wall, an the listened through the playlist of tracks with rouge bass.  The result?  Well moving the speakers away from the wall did change the overall balance toward the "lean" end of the scale.  Plus, almost as proof of concept, the majority of the "rouge" tracks either no longer displayed any of these negative bass artefacts, or at least, the effects were reduced to the point that they were no longer of any real concern.  After much experimentation, I found that actually a 3" (75mm) shift was enough to tame the bass issues, whilst giving a much better overall balance to the sound than was apparent from the 10" (250mm) shift.  I will be leaving the speakers in this position for a while to see how everything sounds after some more prolonged listening.

But there was one track.....   Tricky's "Hell is Around the Corner" (Maxinquaye).  (CD rip, AIR Ethernet)  In addition to sounding a little odd in the very lowest bass with SAM enabled, parts of the track with SAM on produce very large, slow, cone movements.  This is the kind of cone movement you can sometime see using vinyl due to environmental feedback if a subsonic filter is not used.  It is hard to judge, but I would say the cone movement is below the 20hz / audible range.

So some questions.  Firstly, it would be interesting if other users with SAM enabled systems could try this track.  Is it just the SAM / Blade combo that is upset by this track, does it impact some other speakers, large or small?  I am curious!

As a second question.  I am aware that it is possible to enable a "Subsonic filter" in the general settings section of the configurator.  I am thinking of trying this, to see if it tames the unwanted (and slightly alarming) low frequency cone movements that SAM + tacks like "Hell is Around the Corner" can produce.  However, I do wonder if there are any negative to using the subsonic filter.  After all, it does not make sense to compromise 99% of ones listening, just to prevent a minor issue with one or two specific tracks.

My last question, I am sure these cone movements are somewhere in the 10 to 20hz range.  I always thought redbook CD was limited to 20hz?

[Jwg1749]

My last question, I am sure these cone movements are somewhere in the 10 to 20hz range.  I always thought redbook CD was limited to 20hz?

I don't think that's the case. The Red Book spec was designed to cater for the highest frequency humans can hear (c. 20KHz) which, according to the Shannon-Nyquist sampling theorem, requires a sampling rate of (just over) 40KHz. But I don't think the bottom of the range is an issue for the Red Book spec.

It sounds to me as though it would be worth experimenting with the subsonic filter. It may be that SAM is forcing the Blades' woofers to perform a bit too far outside of their design envelope on that particular track.

[Confused]

Thanks Matt, well you live and learn, and if red book CD can go below 20hz, it does make some sense of what I am seeing with the cone movement. However, I don't think SAM is pushing the drivers outside of their design envelope, in fact, one way of eliminating the specific issue with that track is to crank up the volume. I guess SAM is then calculating that the boost at this very low frequency would indeed be out of the drivers range, so it eliminates it.

[amabrok]

Thanks Matt, well you live and learn, and if red book CD can go below 20hz, it does make some sense of what I am seeing with the cone movement. However, I don't think SAM is pushing the drivers outside of their design envelope, in fact, one way of eliminating the specific issue with that track is to crank up the volume. I guess SAM is then calculating that the boost at this very low frequency would indeed be out of the drivers range, so it eliminates it.

I'm more inclined to believe that it is a factor of the SAM protective effect. I.e. A product of elimination rather than addition. And if this assumption is right then I'm not sure what the subsonic filters can offer?


Sent from my iPhone using Tapatalk

[Pim]

With my Dynaudio C1's, and SAM on, the bass drops off when I turn it up too loud so it must be the protection part of SAM that does that. It would be interesting to know what creates the low frequency noises on your track Confused. Have you tried listening through headphones? Is it part of the music? (i.e. does it come with a rhythm or is it random)

[Confused]

With my Dynaudio C1's, and SAM on, the bass drops off when I turn it up too loud so it must be the protection part of SAM that does that. It would be interesting to know what creates the low frequency noises on your track Confused. Have you tried listening through headphones? Is it part of the music? (i.e. does it come with a rhythm or is it random)

I said in my original post that it looks like the kind of environmental feedback that you get with vinyl.  Thinking about this today, I'm wondering if this is exactly what it is.  Not from my turntable, this is a CD rip, but from one of the turntables used to actually perform the track in the first place.  This very likely went unnoticed in the studio, with normal speaker low frequency roll off, but with SAM pushing subsonic stuff to virtually flat  / zero roll off, then the effect is exacerbated and becomes very apparent.

[Pim]

With my Dynaudio C1's, and SAM on, the bass drops off when I turn it up too loud so it must be the protection part of SAM that does that. It would be interesting to know what creates the low frequency noises on your track Confused. Have you tried listening through headphones? Is it part of the music? (i.e. does it come with a rhythm or is it random)

I said in my original post that it looks like the kind of environmental feedback that you get with vinyl.  Thinking about this today, I'm wondering if this is exactly what it is.  Not from my turntable, this is a CD rip, but from one of the turntables used to actually perform the track in the first place.  This very likely went unnoticed in the studio, with normal speaker low frequency roll off, but with SAM pushing subsonic stuff to virtually flat  / zero roll off, then the effect is exacerbated and becomes very apparent.

There was a story going around at the time that Philips introduced the CD that they had made a recording that had some sort of rumble that they couldn't quite identify. It turned out that it was a train or subway that was close to the recording studio at the time of the recording. Of course it could just have been made up by an advertising company... Maybe you could sell your 'problem' to Devialet to be used as a sales pitch 

[markush]

What are your final thoughts on using the subsonic filter?

[David A]

I tried using the subsonic filter for a while but went back to not using it. It cuts the signal below 20 Hz but it it's going to cut anything then there has to be content below 20 Hz. There is very little music with content below 20 Hz, some organ music and some synthesiser music, some electronic sounds in soundtracks and experimental music, but I'm not listening to that sort of content and my source is digital so I don't have to worry about the effect of low frequencies on vinyl playback. If whatever you're playing doesn't have any frequency content below 20 Hz then the subsonic filter isn't going to have an audible effect.

The subsonic filter is an answer to a problem. If you don't have that problem they you don't need the subsonic filter. Why add processing to the signal if it's processing that you don't need? I think people should use it if they need it but not use it if they don't need it.

[audio_engr]

I tried using the subsonic filter for a while but went back to not using it. It cuts the signal below 20 Hz but it it's going to cut anything then there has to be content below 20 Hz. There is very little music with content below 20 Hz, some organ music and some synthesiser music, some electronic sounds in soundtracks and experimental music, but I'm not listening to that sort of content and my source is digital so I don't have to worry about the effect of low frequencies on vinyl playback. If whatever you're playing doesn't have any frequency content below 20 Hz then the subsonic filter isn't going to have an audible effect.

The subsonic filter is an answer to a problem. If you don't have that problem they you don't need the subsonic filter. Why add processing to the signal if it's processing that you don't need? I think people should use it if they need it but not use it if they don't need it.

+1 .. i believe in "the lesser the better" approach

now that you seem to be enjoying the ER & have settled down with it, I'm considering that route.