Vinyl Record Inner-Groove Distortion (A Simple Explanation)

Marc HenshallTech Talk3 Comments

While vinyl records have plenty to offer, both sonically and from a listening experience standpoint, they also come with some trade-offs. One of the most commonly cited but also misunderstood trade-offs is a phenomenon known as inner-groove distortion (also referred to as end-of-side distortion.

Inner-groove distortion is an audible deterioration in sound quality that sometimes occurs when playing tracks close to the end of each side. Some would call it a design flaw, for others, it’s just part of the vinyl experience. But what causes it? Let’s dig (briefly) into some light physics…

inner-groove-distortion

The fundamental cause of inner-groove distortion is the progressive reduction of linear resolution as a record progresses. Put another way: there is more vinyl per second available at the large-diameter beginning of the record than exist at the smaller-diameter toward the end of each side. Subsequently, the wavelengths become gradually shorter and more compressed (like an accordion) as you get closer to the records centre. These more condensed grooves are much harder for the stylus to track accurately.

The problem is most noticeable at higher recorded volumes (particularly if there’s a lot of high-frequency energy). Mastering engineers will attempt to mitigate end-of-side distortion by pressing quieter songs, with moderate bass and lower HF energy towards the center of each side. Alternatively, they will restrict the playing time, or spread an album over two discs to avoid inner grooves.

Even when taking linear resolution into account, there is still the issue of cartridge and stylus alignment. The machines used to cut records operate on a parallel basis, meaning the cutting stylus is perfectly aligned from start to finish. Turntables, on the other hand, use a pivoting tonearm, which can only line up correctly at two points across the record surface (it’s a fact of geometry). A properly configured, high-quality turntable with a minimum 10inch tone arm can reduce tracking errors significantly, but tracking errors will always be most noticeable at the inner grooves – thus further encouraging end-of-side distortion.

Various attempts have been made to mitigate end-of-side distortion – such as purposefully misaligning the cartridge to improve inner-groove tracking at the expense of outer grooves, however, the fact remains it will always be a compromise.

With all of this in mind, it would be easy to dismiss vinyl as a flawed medium, which of course it is. But that doesn’t make vinyl any less relevant – far from it. In many cases, inherent distortion in the vinyl format is what draws people in; often referred to as “analog warmth,” what we’re actually experiencing is the analog medium imparting sonically pleasing distortion. The line at which pleasant, warming distortion becomes irritating distortion will be different for everyone, but some distortion is just part of the deal with vinyl.

The best course of action is to invest in a good turntable and ensure you configure it precisely. After all, if you play records on a poorly setup deck, the inner grooves will suffer the greatest damage.

How to Set up Your Turntable

There are many variables in turntable setup. For the purpose of this article, we’ll take a look at the fundamentals: tracking pressure, cartridge alignment, and anti-skating. By getting these set correctly, we can greatly reduce tracking errors, and ultimately, achieve better sounding records.

Tracking Pressure (downforce)

The counter weight on the end of your tonearm is used to apply the correct amount of pressure in agreement with the manufacturer’s recommendations. (Check your cartridge manual for the proper weight).

Here’s how to apply the weight specified:

1: Start by setting the turntable’s anti-skating dial to zero (you don’t want any additional weight on the tone arm at this stage).

2: Use the weight on the back of the arm to balance the tonearm until it floats on its own.

3: Turn the number dial (which turns independently from the weight itself) until it reads zero. The tonearm should still be floating freely, and you’re ready to apply the weight specified in your cartridge manual.

4: Turn your counter-weight until the dial reads the correct number. Once set, your cartridge will track at approximately the right pressure.

(Refer to your turntable manual for details on how your counterweight scale represents downforce. In my case, one mark on the scale represents 1 mN (0.1g). To apply the 1.75g required for my cartridge, I simply set the counterweight to 17.5 mN.)

5: To ensure a more accurate weight, adjust using a stylus tracking force gauge.

Cartridge Alignment

As determined earlier, the cartridge can only correctly align with the record grooves at two points across the record. It is critical we achieve correct alignment at these points to ensure minimal tracking errors across the remaining surface area. For this application, I recommend using a cartridge alignment protractor.

Step 1: If your headshell allows for overhang adjustment (that’s the distance between your center spindle and the stylus tip) make sure you adjust the length in agreement with your turntable manual. Mine specifies 22mm.

overhang-test

Step 2: Place your cartridge alignment protractor on the platter, and carefully drop the stylus tip onto the first alignment point. The metal cantilever holding the stylus tip should be parallel with the guidelines on your protractor – if it isn’t, carefully adjust the headshell screws and adjust until everything lines up. (The alignment tool I’ve linked comes with a mirror to help you achieve accurate results). You can also use the front and side of the cartridge body to help you achieve perfect alignment with the horizontal and vertical lines on your protractor.

Step 3: Use the second point to check your results. If all is well, the cartridge should align correctly at both points.

Anti-skate

Essentially, the purpose of anti-skate is to counteract the force naturally pulling your stylus toward the record spinal. This force encourages the stylus to rid the inner edge of record grooves and prevents it from sitting centrally. The result is decreased sound quality and increased record wear.

The best way to test anti-skate is using a test record, which will have a blank groove purposely intended for setting anti-skate. When the correct weight is applied, your stylus will sit centrally in the blank space without rocking or riding toward the center spindle.

The following video below is one of the clearest explanations of anti-skate I’ve stumbled across on the web:

Final adjustments: Vertical Tracking Angle (VTA) & Azimuth

With the above adjustments made, the final adjustments you want to check are Azimuth and vertical tracking angle.

First up, azimuth refers to the how the cartridge is aligned from a horizontal perspective. When the azimuth is set correctly, your cartridge is 100% level over the record grooves. In other words, the cartridge isn’t tilted left or right and hovers evenly over the record surface.

Next up, vertical tracking alignment, or VTA. This final alignment refers to the whole tone arm level across the record surface. You want the tone arm distance from the record to sit evenly from front to back. That is, the front (cartridge end) should not sit lower than the back (pivot end), and vice versa. Some turntables will allow you to correct uneven VTA by raising or lowering the tonearm at the pivot end. If your turntable does not feature such an adjustment, you can use a combination of cartridge washers, and placemats to adjust your tonearm height from the cartridge end.

Levelling the Turntable

Last but not least is turntable level. Once you’ve finished setting up a turntable, it is imperative you place it on an even surface – failing to do so could through off your carefully aligned deck and ultimately void the entire process. Start with a solid, even surface and use a spirit level to help you measure any fine adjustments.

To help you get to grips with the adjustments I’ve described, I recommend also watching the following YouTube video:

The Bottom Line

I love vinyl records, but I’m under no illusion when it comes to the compromises. On paper, digital is superior in almost every way from a technical standpoint. However, specifications can also be deceiving, and current mastering practices often lead to vinyl releases having greater dynamic range than their digital counterparts, which is ironic.

For me, digital is very convenient, but it’s also clinical – both from an audible and tangible perspective. I listen to analog and digital formats, but there’s just something extra special about vinyl – warts and all. End-of-side distortion is arguably one of the peskiest drawbacks, but you can reduce it by carefully configuring your setup. Do so, and your records will reward you with beautiful sound for many years to come.

Liked it? Take a second to support Sound Matters on Patreon!