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Soundsmith explains RIAA and Strain Gauge

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Posted on December 11, 2010 at 13:48:58
Retipper
Manufacturer

Posts: 179
Location: New York
Joined: December 17, 2006
 I get so many requests to explain why the Soundsmith Strain Gauge does not need RIAA, that I thought I would post here at AA a recent response I gave to a reviewer in the effor to present a simplified explanation, BUT from a new persepctive. It is my hope that to those who have not understood it before that this "simplifed" view will be of help to them in understanding this.

The purpose if this is NOT to provide a detailed explanation of why RIAA is used, but to explain why displacement devices (Strain Gauge, ceramic, etc...) work fairly well (please don't attack that statement anyone)without needing to employ the RIAA playback EQ. This meant to open a BASIC discussion if needed, not an attack of the priciple. Many thanks for that.

The Strain Gauge cartridge does not use or require an RIAA playback filter because it inherently plays the RIAA recording EQ curve used on the record without the need to employ such. This is because the RIAA recording curve used to make the original master recording with a magnetic cutter head COMPENSATES for that cutter head's velocity response and results in a groove of basically equal “displacement” for an amplitude flat input signal. How does that happen? Simply. Without RIAA, the "velocity" response of the magnetic cutter head would normally cut a large displacement groove for low frequencies, and less so as the frequency rises. One could actually cut a record without RIAA with a magnetic cutter, and play it back with a magnetic cartridge WITHOUT using RIAA playback, and get a perfectly flat response, BUT without the benefits of RIAA (more recording room, lower noise, etc,...).

By using RIAA during recording, which LOWERS the amplitude (and therefore displacement of the groove) as the frequency lowers and raises it as the frequency increases, it "COMPENSATES" for the natural displacement differences of a magnetic cutter head's response and RESULTS in a basically equal displacment groove, for a flat input signal!

Since normal mangetic cartridges are velocity sensitive devices (whose output is sensitive to velocity), they need the RIAA inverse filter to result in a flat playback response of a groove cut with an RIAA recording curve and a magnetic cutter. However, since the Strain Gauge is a DISPLACEMENT sensitive device, it automatically produces a basically flat response from a RIAA encoded groove, which as stated above, is a basically equal displacement recorded groove.

The Strain Gauge cartridge is a displacement device, producing an output that is dependent and directly proportional to the amount of displacement of the stylus, NOT the velocity, as in magnetic cartridges. A magnetic cartrdige's output voltage is dependent on the velocity of the stylus, like any magnetic generator.

The Strain Gauge therefore inherently plays the RIAA encoded groove nearly correctly. If one inspects the RIAA EQ, one will discover that there are discrepancies that occur where a displacement type cartridge deviates from a perfectly flat playback of the recorded RIAA groove, and therefore will not produce a perfectly flat response.

Attempts made in the distant past to absolutely correct Strain Gauge cartridges for any amplitude anomaly have required equalization circuits, which not only can require adding circuitry, but also introduce unwanted phase or time shifts. It is the Soundsmith’s belief that human hearing is much more forgiving of amplitude errors than short range time errors, so we have made what we beleive to be acceptable and minimal efforts to correct for any amplitude deviation from absolute flatness.

Peter Ledermann/Soundsmith

 

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Thanks,, posted on December 11, 2010 at 16:16:43
Nasty
 that's a bit of an education for me. I've never heard a strain gauge cartridge but I'd guess a level of clarity above "normal" without the equalization circuitry in place?

 

Thanks for an excellent explanation..., posted on December 11, 2010 at 18:38:01
John Elison
Audiophile

Posts: 24048
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 I have a feeling that some people might not know the definition of "velocity" as it applies to phono cartridge operation. Therefore, I just want to add a little to your excellent explanation by defining the term "velocity" relative to this discussion.

The term "velocity" refers to the back-and-forth and up-and-down motion of the stylus in the groove. If you measure the total distance the stylus wiggles back-and-forth, and divide that distance by time, you get "stylus tip velocity." In other words, a stylus tip velocity of 5-cm/s means that the stylus is moving back-and-forth in the groove a total distance of 5-centimeters every second. This is also known as "groove velocity."

Refer to the picture below for a graphic representation of a sinusoidal groove like those found on test records.

Velocity is proportional to the product of displacement and frequency. Displacement is the distance the stylus is pushed out from its rest position. It would be equivalent to the groove amplitude in the picture below. Frequency is the number of times per second the stylus moves back-and-forth in the groove.



For example, suppose the groove amplitude is 12.5-µm (0.00125-cm) and frequency is 1000-Hz. The average groove velocity would be 5-cm/s. In each cycle the stylus moves a distance of four groove amplitudes and there are 1000-cycles in 1000-Hz. Therefore:



Groove velocity and stylus tip velocity mean the same thing. Normally we are not concerned with average velocities, but we are more concerned with peak velocities and RMS velocities. For a sinusoidal groove:



As Peter explains in detail, the output from magnetic cartridges is proportional to groove velocity whereas the output from strain gauge cartridges is proportional to groove amplitude only.

Best regards,
John Elison

 

RE: Soundsmith explains RIAA and Strain Gauge, posted on December 11, 2010 at 21:04:07
coffee-phil
Audiophile

Posts: 1447
Location: Shingle Springs CA
Joined: January 7, 2010
 Most of what Peter said in his post makes sense to me. From 50 Hz to 500 Hz and from 2121 Hz up RIAA records are recorded constant amplitude so an amplitude responding cartridge such as a ceramic or strain gauge will have the correct response through those parts of the spectrum however from 500 Hz to 2121 Hz the records are cut constant velocity so the response will fall 6 dB / octave over those ~ two octaves. He points that out but says it is a good trade to accept that rather than use EQ to fix it. For a cheap system with a ceramic cartridge who would argue the point but for a high end system using a strain gauge I have to believe the effort would be justified. He points out that the EQ will introduce phase shift. This of course is true but the points of inflection in the recording process (500 Hz and 2121 Hz) introduce phase shift as well. I would think one would want a network on the playpack end which is the inverse of the record EQ. This network wont be the same as the one used with a velocity responding cartridge.

Phil

 

A couple of questions..., posted on December 11, 2010 at 23:11:52
tubesforever
Manufacturer

Posts: 10505
Location: Great Basin
Joined: May 7, 2005
 Peter, I have not heard your SG cartridges so my comments are limited to the Panasonic and Sau Win cartridges I heard back in the day.

I am a fortunate guy who owned both Sau Win's SG-1 and SG-2 cartridges. They commanded some of the best bass response I have ever experienced in LP playback. Also their midrange was exemplary. However the upper mid range and the highs were compromised as compared to an equally priced MC of the day.

I know that John Bedini had built a special transducer box for the SG cartridge that at the time sold for about $1000.00. I remember the complete SG 2 at the time was selling for around $550-600. The Bedini transducer sounded amazing during the time I heard it play. I remember it playing an improved frequency response.

Does the RIAA compensation in the LP mastering account for any or all of the perceived upper mids and high end response differences between the MC and SG?

Could a selectable EQ be as easily adapted to the SG tranducer as it is to a standard phono preamp to better system match or correct for the variant eq used by the different record labels?

As an example, Deccas and Londons generally sound warm in comparison to an RCA's RIAA. Capital and DG albums often sound brighter than the RIAA. I use such a switch in my phono section to bring these closer to an ideal frequency response.

Thanks for the opportunity to dialog around the SG cartridge.

Jim Howard



"Help support our school's Music programs"


 

RE: Soundsmith explains RIAA and Strain Gauge, posted on December 12, 2010 at 03:17:42
Werner
Audiophile

Posts: 2123
Joined: September 30, 1999
 "Attempts made in the distant past to absolutely correct Strain Gauge cartridges for any amplitude anomaly have required equalization circuits, which (...) introduce unwanted phase or time shifts."

I am sorry, but this is simply not true.

Record cutters, cartridges, preamps, ... all are minimum phase systems. This means that the phase response can only be flat (i.e. constant delay and no frequency-dependent time distortion) when the total system frequency response is flat, and vice versa.



And then you wake up and realise that your classmates of old ... are running most of the TV shows.

 

RE: Thanks,, posted on December 12, 2010 at 06:01:04
Retipper
Manufacturer

Posts: 179
Location: New York
Joined: December 17, 2006
 I would like to address a few issues, and remind some to read my English carefully. When I use the word "can", it means just that. It does not mean "always", so please don't read "can" as always. Thanks.

Thank you John for the excellent post, as always. Great to meet you at RMAF.

Regarding amplitude and phase coherence, I would point out that there is an extended blog on another site wherein after MANY posts, it is FINALLY realized that the mechanical realization of the actual design of a Strain Gauge has the final say, and personally having built many Strain Gauge cartridges (and manufactured and rebuilt thousands of magnetics over that 35 years), leaves me in the fixed position of vehement agreement.

Looking at the mechanics of a cartridge cross-eyed will modify its response. This is why that blog finally comes to rest indicating that Matsushita made many models of SG cartridges, all with different amplitude and phase responses. I will not tell you how many prototypes and how many man-hours I have spent in pursuit. But if those who speak of perfect amplitude being the only factor for perfect phase, I would argue that point, and indicate that the rheology of materials results in transient performance that conflicts with steady state performance, and therefore one "design" cannot be perfect for all waveform situations. We all know that cartridges sound differently, even those of the same model, due to differences in manufacture both within and outside of the control of that manufacturer. I am not saying that flat is bad, so I would beg you to not attribute that to me. What I AM saying is that flat is not everything by any means. If it were, all "flat" cartridges and precision preamps would sound the same. They don’t. This clearly indicates that a cartridge with a radical change in design can sound radically different. What radical change? How about moving mass....

For those who agree with me on this matter, I will say that the ultra-low moving mass of the Strain Gauge is a major factor in its enjoyment. Consider the following: If you want best statistical road contact of a tire on a sports car, you lower the mass of the tire and rim, and fine tune the suspension. The same goes for a stylus/cantilever. There are those who may not think of "analog" phono cartridges as being digital. They are. They take "samples" of the groove wall as the stylus "bangs" its way down the groove. The stylus does not stay in intimate contact, for many reasons. Lowering the moving mass helps greatly. It raises the resonant frequency, and can lower the amplitude of resonance by allowing the damping and suspension to be much more effective. This means a higher sampling rate of the position of the groove wall. More samples, more detail. Different sound.

My purpose in pointing this out is that while some are myopically focused on one or two aspects only of phone cartridge response, they must consider taking into account that everything matters all the time. Whereas one person may willingly trade off absolute flatness of amplitude and phase for errors that are smoothly spread out and potentially not as objectionable as those that are confined to small regions, another will absolutely not for religious reasons. A design that offers greater "sampling" rate may be far more acceptable to some, and not others. The tiny errors that result in perturbations that are not measurable, but highly audible, can result in loss of detail and image presentation. Look at digital, if you will, for tiny but very "listenable" differences. Often, these are the major factors that make one (product) cartridge preferable over another. Please note that one hardly ever hears of speakers being rejected due to loss of absolute phase and perfect flatness. They are accepted or rejected based on how well they behave on average to the listener, based almost solely on their preference, in their acoustic environment, with their associated equipment. Such is the life of a transducer and its potential acceptance.

In terms of why certain records sound far different, and often unexpectedly so with the SG, I can say that this has been an effect that Richard Majestic and I noted over the past 35 years. There are many possible explanations for this, but the one that makes the most sense to us is that the detail retrieval possible with the SG of some records
is desirable, and of others, at times, not. There are times when we don't want to hear the all the errors in the recording chain that made the record, and we want to gloss them over.

Then, there are other times.............


Peter Ledermann/Soundsmith

 

Interesting frequency response..., posted on December 12, 2010 at 10:07:36
John Elison
Audiophile

Posts: 24048
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 I decided to look at the RIAA recording characteristic compared to a constant amplitude playback characteristic relative to the constant velocity vinyl world in which we live. When we combine the RIAA curve with the constant amplitude playback curve we get a theoretical frequency response curve pretty much identical to your description of Sau Win's SG-1 and SG-2 cartridges.

> They commanded some of the best bass response I have ever experienced in LP playback. Also their midrange was exemplary.
> However the upper mid range and the highs were compromised as compared to an equally priced MC of the day.



 

RE: Thanks,, posted on December 12, 2010 at 11:23:32
Solidcore
Audiophile

Posts: 374
Joined: April 19, 2001
 Thanks for shearing your knowledge. Your postings are most interesting and informative !!

Rgds Jan

 

Boy that graph sure does sum up the sonics of the SG1&2, posted on December 12, 2010 at 16:20:01
tubesforever
Manufacturer

Posts: 10505
Location: Great Basin
Joined: May 7, 2005
 It was cool for a teenager needing good bass with the volume low. I got in less trouble ;-)

After a year to two years, I found I needed more balance. After finding some affordable and excellent sounding MC's I have never looked back.

I wish I knew how the Bedini box measured up in comparison to Sau Win's box. It sounded really promising. Perhaps I will have an opportunity in the future to hear how Peter is handling SG.

Thanks for posting the graphs John.

Jim

"Help support our school's Music programs"


 

RE: Interesting frequency response..., posted on December 12, 2010 at 17:22:07
Retipper
Manufacturer

Posts: 179
Location: New York
Joined: December 17, 2006
 Dear John;

It is interesting, but does not represent the real world readings taken from many strain gauge cartridges, both with EQ, as well as without. When I worked at RAM Audio, the Strain gauge system we produced with the Matsushita cartridge was very flat and had no EQ; no SG system could ever be sold with a 20dB bass boost and such a huge high cut as you show; the SG systems simply do not create a curve such as this. I have never taken a reading like this from any strain gauge, and the extremes represented here by this mathematical "representation" do not match the real world measuremnts by a long shot.....if so, it would be completely unlistenable by any standard, and it obviously is not.....you have heard it in my room at two shows, with minimal EQ in the midband only....

All the best - peter

 

RE: Interesting frequency response..., posted on December 12, 2010 at 18:45:06
John Elison
Audiophile

Posts: 24048
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 Hi Peter,

It's all in the mathematics. The frequency response in my graph represents a theoretical cartridge that responds to amplitude deflection only. Yes, it would have a very unreasonable frequency response when playing an RIAA encoded LP. I'm sure you've done the math, too.

It would be very interesting to see an actual frequency response graph of your strain gauge cartridge playing an RIAA test record like Denon's XG-7005. If you're interested, I'd love to measure your strain gauge.

These are the kind of frequency response and crosstalk response graphs that I measure from my own cartridges.

Best regards,
John Elison



 

RE: Interesting frequency response..., posted on December 12, 2010 at 22:34:39
Werner
Audiophile

Posts: 2123
Joined: September 30, 1999






Here is the full SG200 system as measured by Hifi News:


And then you wake up and realise that your classmates of old ... are running most of the TV shows.

 

Interesting! Thanks, Werner...., posted on December 13, 2010 at 11:27:41
John Elison
Audiophile

Posts: 24048
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 Did they mention which test record was used?

I own test records with constant amplitude sweeps up to 500-Hz and constant velocity sweeps from 500 to 20,000-Hz. However, for my purposes I like to use an RIAA sweep from 20 to 20,000-Hz while measuring frequency response at the output of my phono stage in order to observe the performance of my entire vinyl front-end. I guess I'm wondering why they split the response test into two parts if they used an RIAA sweep, which is normally continuous from 20-Hz to 20-kHz

Thanks,
John Elison

 

RE: Interesting! Thanks, Werner...., posted on December 13, 2010 at 17:05:50
0luke1


 
The science is interesting, but I'm listening to the Cannonball Quintet "in San Francisco" right now - on my SoundSmith SG (Basis 2500, Vector 4, c22, MC275 Spendor c8e).

All I can say is the immediacy of the here and now on this album is totally enjoyable.

 

Yeah, I really liked it when I heard it, too. /nt\, posted on December 13, 2010 at 17:14:35
John Elison
Audiophile

Posts: 24048
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004

 

RE: Interesting! Thanks, Werner...., posted on December 14, 2010 at 10:10:02
Werner
Audiophile

Posts: 2123
Joined: September 30, 1999
 Nope, no details. But all cartridge measurements at HFN are presented this way.

See link for more, but you have to register. Which is painless.

And then you wake up and realise that your classmates of old ... are running most of the TV shows.

 

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