Warp filtering.

[Mark S.]

I was taken aback when playing a 24/96 recording of a 45 RPM audiophile (double) LP and happened to see the bass cones in my diminutive Oli Roth RA1's visibly pistoning away with the record warps.

On trying a few test wavs, even practically DC (a few Hz) was faithfully being passed to the speakers.

I happen to be using an old (!) Indeed Labs Tripath TA2020 at the moment (don't care, it sounds lovely at 'late-night' volume levels) and the RA1's are only 83 dB/W. Obviously I don;t want its hilariously small 9+9W being wasted reproducing infrasonic frequencies.

APO Equaliser to the rescue - although it's set to a rising curve below c. 180 Hz (the RA1's start rolling off at 80Hz) and I do get audible bass down to c. 32Hz with room reinforcement (the RA1's rear ports are about 6" from the wall and my listening position has my head about a foot from the opposite one c. 12 feet way), I've now set 25Hz to 0dB and 20Hz to -30dB and no more bass cone pistoning.

TLDR - always use APO or your equaliser of choice to make a STEEP high pass filter below a sensible frequency for 'flea watt' amps and small speakers.

 

[MaxwellsEq]

I was taken aback when playing a 24/96 recording of a 45 RPM audiophile (double) LP and happened to see the bass cones in my diminutive Oli Roth RA1's visibly pistoning away with the record warps.

On trying a few test wavs, even practically DC (a few Hz) was faithfully being passed to the speakers.

I happen to be using an old (!) Indeed Labs Tripath TA2020 at the moment (don't care, it sounds lovely at 'late-night' volume levels) and the RA1's are only 83 dB/W. Obviously I don;t want its hilariously small 9+9W being wasted reproducing infrasonic frequencies.

APO Equaliser to the rescue - although it's set to with a rising curve below c. 180 Hz (the RA1's start rolling off at 80Hz) and I do get audible bass down to c. 32Hz with room reinforcement (the RA1's rear ports are about 6" from the wall and my listening position has my head about a foot from the opposite one c. 12 feet way), I've now set 25Hz to 0dB and 20Hz to -30dB and no more bass cone pistoning.

TLDR - always use APO or your equaliser of choice to make a STEEP high pass filter below a sensible frequency for 'flea watt' amps and small speakers.

A better approach is to filter everything from vinyl below 30Hz, since there is nothing of any value below that frequency.

 

[Mark S.]

A better approach is to filter everything from vinyl below 30Hz, since there is nothing of any value below that frequency.

Indeed (!), but actually with everything if your system is as Lilliputian as mine.

I now get surprising levels out of it with some of my favourite bass-test recordings, for e.g. Simon Phillip's Another Lifetime (a lot of kick and floor toms, Anthony Jackson's ridiculous six-string 'contrabass') and Daft Punk's Random Access Memories

 

[Chrispy]

Never kept warped records for long....

 

[Mark S.]

BTW, posting this on the notionally 'analogue' forum might seem odd, but I'm assuming many do what I used to, record vinyl digitally.

Some phono stages had un-spec'd warp ('subsonic') filters, some had switchable ones, but I'm not sure how well such steep LF high-pass analogue circuits work.

 

[Mark S.]

Never kept warped records for long....

Vinyl is never perfectly flat, there is always 'infrasonic' output from the cartridge.

 

[Chrispy]

Vinyl is never perfectly flat, there is always 'infrasonic' output from the cartridge.

Nor is it very well punched in the center at times. Just a couple reasons why I don't bother with vinyl much these days. I can't say I've gotten any particular cone movement from my fairly flat ones otoh....then again hard to imagine your speakers having noticeable cone movement in infrasonics now that I look them up. Maybe the transcription wasn't so "audiophile"? YMMV.

 

[Mark S.]

Nor is it very well punched in the center at times. Just a couple reasons why I don't bother with vinyl much these days. I can't say I've gotten any particular cone movement from my fairly flat ones otoh....then again hard to imagine your speakers having noticeable cone movement in infrasonics now that I look them up. Maybe the transcription wasn't so "audiophile"? YMMV.

Yes, but when it's good it's very good. I'm old enough to remember playing the UK first press of Crime Of The Century on my dad's system (which included a Decca FFSS C4E on a unique Worden 'tangential tracking' arm) - the story behind the cutting and pressing of that album is fascinating. And there were many other revelatory moments.

Re. "not so audiophile" - the recording wasn't mine and was obviously a 'raw' transcription done via a phono stage with no 'warp filter' of any kind, and that cone flapping is inevitable when playing back through any system which is also filterless. Believe me, the movement isn't subtle. I actually tried a 2 (two) Hz wav and watched in amazement as the 3.5"/ 9cm cones slowly pulsed a good cm back and forth.

 

[Mark S.]

I'm so long out of the vinyl game that I completely forgot about 'arm/cartridge resonance' (I always thought a better word is 'oscillation'), which can also add large amounts of infrasonic to the signal.

The only solution was and is "the Trough" as (almost) perfected by the late, great Max Townshend.

 

[MaxwellsEq]

The only solution was and is "the Trough" as (almost) perfected by the late, great Max Townshend.

As invented at Cranfield Tech. I have the patent somewhere. But, the trough can't put music back where there is none.

I now get surprising levels out of it with some of my favourite bass-test recordings, for e.g. Simon Phillip's Another Lifetime (a lot of kick and floor toms, Anthony Jackson's ridiculous six-string 'contrabass') and Daft Punk's Random Access Memories

There's almost no music on vinyl below 30Hz, so the tunes you are hearing is content from above there.

Some phono stages had un-spec'd warp ('subsonic') filters, some had switchable ones, but I'm not sure how well such steep LF high-pass analogue circuits work

They are mostly fine. They are certainly a vast improvement on playing a load of non-musical resonance noise.

 

[Mark S.]

As invented at Cranfield Tech. I have the patent somewhere. But, the trough can't put music back where there is none.

There's almost no music on vinyl below 30Hz, so the tunes you are hearing is content from above there.

They are mostly fine. They are certainly a vast improvement on playing a load of non-musical resonance noise.

Max was a student of Professor Dinsdale at Cranfield when the latter invented and experimented with the Trough (he was actually trying to tame Decca FFSS cartridges) and always gave him credit, Max put the concept into production. It has a profound benefit in many ways, not least completely negating LF spuriae from arm/cartridge resonance and much reducing injected LF from the motor, bearing and environment - the famous "blackness" of Townshend decks.

The improvement in SPL's after implementing low-pass filtering I was referring to is due to not passing LF (from any signal source) that's completely beyond my amp/speaker/room response, and I can definitely crank it somewhat louder than previously. It hadn't occurred to me to try it until I saw that warp-induced cone flapping.

 

[Chrispy]

Yes, but when it's good it's very good. I'm old enough to remember playing the UK first press of Crime Of The Century on my dad's system (which included a Decca FFSS C4E on a unique Worden 'tangential tracking' arm) - the story behind the cutting and pressing of that album is fascinating. And there were many other revelatory moments.

Re. "not so audiophile" - the recording wasn't mine and was obviously a 'raw' transcription done via a phono stage with no 'warp filter' of any kind, and that cone flapping is inevitable when playing back through any system which is also filterless. Believe me, the movement isn't subtle. I actually tried a 2 (two) Hz wav and watched in amazement as the 3.5"/ 9cm cones slowly pulsed a good cm back and forth.

Vinyl can be good, but there's better. I'm probably near your age if not older. Do remember some of the various tech used for linear tracking, but seems riddled with issues, so never bought into personally, tho used a few at times.

I've played vinyl for a long time, and just never found warped records worth bothering with at all for a few reasons. Not had infrasonic issues otherwise.

 

[Mark S.]

Vinyl can be good, but there's better. I'm probably near your age if not older. Do remember some of the various tech used for linear tracking, but seems riddled with issues, so never bought into personally, tho used a few at times.

I've played vinyl for a long time, and just never found warped records worth bothering with at all for a few reasons. Not had infrasonic issues otherwise.

We're dealing with an archive or legacy of recorded music. If it was recorded before c. the late 1980's, let alone back in the 70's and beyond we have the analogue tapes or the records they were pressed from. Paradoxically the tapes are now sometimes in such bad condition (literally worn out) or lost (perhaps leaving only generational copies) that original release records in good condition are actually the best versions that remain in existence. Some hold the opinion that any Red Book CD release (including ancient ones made closer to the age of some of these 'legacy' recordings) is better than a good LP one, that's not my view.

 

[Risto_H]

I'm so long out of the vinyl game that I completely forgot about 'arm/cartridge resonance' (I always thought a better word is 'oscillation'), which can also add large amounts of infrasonic to the signal.

The only solution was and is "the Trough" as (almost) perfected by the late, great Max Townshend.

In my opinion, there are other pretty good methods to suppress problems caused by warped records in addition to this. I'll just make a short list (not in any particular order) here:

1. Damping brush added to the cartridge like Shure did with a few models
2. Servo tonearm that tracks the surface actively. Denon and Sony did some nice examples that actually work.
3. Mixing low frequency content to mono (under certain turnover frequency) in RIAA. Classic Audio (Michael Fidler) is one good example.
4. A more novel version of this has been invented by Wyn Palmer. His RIAA design avoids possible problems with channel separation and LF response while maximizing the warp filter efficiency.

Personally I use a Denon DP-51F with Sure V15 Type IV and see absolutely no harmful bass cone movement, even with a RIAA that does not have any kind of subsonic filter.

I might add that a simple high-pass "subsonic" filter is a bit brutal method to achieve warp filtering since it unnecessarily affects the LF phase up to 200 Hz even though it is true that an LP seldom has any music signals < 30 Hz. Also bass content on the LP surface is lateral while warps are vertical. That is the reason why a proper warp filter is more optimal method and only concentrates on removing signal components that result from vertical forces to the needle.

 

[Buck_Rogers]

This turntable platter I machined is actually "Bowl shaped".

Just a tiny amount, Enough to remove 95% of all warps.

Works great. Copied the idea from Goldmund about 25 years ago.

 

[antennaguru]

This turntable platter I machined is actually "Bowl shaped".

Just a tiny amount, Enough to remove 95% of all warps.

Works great. Copied the idea from Goldmund about 25 years ago.

Very nice turntable! You have done well with your concave platter shape and clamp to flatten records as best as can be done. There are some other approaches that work well too (e.g., Townshend Rock, Oracle), but some warps are not so simple and cannot be completely eliminated (e.g., edge warp). The problem that you will experience with warped records on your system is the warp-wow due to the apparent stylus rake angle changing rather dramatically as the very short effective tonearm length of your tonearm exacerbates that. Clearaudio, Souther, and Revox ignored that issue, while also ignoring that other much more successful linear tracking tonearms used a more reasonable length (longer) tonearm to mitigate the warp-wow issue.

I own two linear trackers myself, a Goldmund and a B&O, which both have quite longer tonearms. However, for playing a rare record that is quite visibly warped my preference is actually to use one of my turntables that has a 12" long radial tonearm, as that even longer tonearm mitigates SRA warp-wow by simple geometry.

 

[Buck_Rogers]

I have so few warped records and have never heard any wow ever.

The conical shape allows almost continuous contact between LP and platter.

My daily has a PolyCarbonate mat with same shape.

Still be best sounding table and arm I've ever used. Miles beyond my SME V.

Have designed, repaired, modded and listened to many hundreds of turntables.

Makes my 10,000$ digital setup sound like a rusty nail... lol.

Buck

Poly mat platter.

Platter bottom view:

Fluid damped cartridge and On the Fly VTA, picture from 2010: