Benny Audio writes: “WOW & FLUTTER – introduction. I believe that a turntable is a simple device, regardless of how complicated it may seem. Putting aside issues related to aesthetic needs or satisfying one’s ego, a turntable has only two functions:
- Function 1 related to the drive – spinning the platter (and this is where I will focus)
- Function 2 related to the tonearm – not interfering with the cartridge (this will be discussed another time)
Both of these functions are susceptible to the degrading effect of mechanical disturbances. Moreover, they are often the source of these disturbances.
Mechanical disturbances were already described by Poul Ladegaard in his 1977 article titled “Audible Effects of Mechanical Resonances in Turntables.”
The author includes the following in mechanical disturbances: tonearm resonances, hum, and wow & flutter.
Let’s focus on the main subject of this brief text – wow & flutter, which refers to the sonic effect of the turntable’s imperfections as a whole device. Wow refers to the lower frequency fluctuations (up to 4Hz), while flutter refers to the higher frequency fluctuations (above 4Hz). Since we are examining a sonic effect, W&F pertains not only to the drive but to the entire system, which I will elaborate on shortly. Wow is audible, while flutter affects sound aspects that are not directly audible (attack, decay, clarity, interaction with the environment, sound fading, etc.).
How can we examine W&F?
During the golden age of vinyl, the only available and simultaneously the best method to study this phenomenon was through sound analysis resulting from playing a constant signal (1000 Hz or 3125 Hz) from a so-called test record. This signal was examined using dedicated devices, processed, and resulted in some information. Such records were, and probably still are, produced. The problem is that these are not some magical records made in a laboratory. They are records cut and pressed just like all others and are, by definition, far from perfect.
In the referenced article, the author professionally describes what was obtained in the graphs when studying W&F through the analysis of the signal from the test record. He demonstrates that W&F distortions resulted from:
- Record off-centering (did I mention that records are terrible?)
- Elliptical grooves
- Tonearm resonances
- Hum (grounding issues)
- Drive imperfections (to a minimal extent – probably because the drives back then were really excellent).
The author’s unequivocal conclusion in studying W&F using a test record and relating the results to the quality of the drive is as follows – audible W&F disturbances pertain to the drive only to a small extent, making it difficult to relate the results to the drive.
Even in 1977, experts knew that examining the drive by playing a test record was pointless, yet this method still has many adherents.
Summarizing the “test record” method – why is it not worth trusting W&F measurement results?
- Each test record is different and has different distortions.
- Each test record is made on a different cutting lathe, so it is at best as accurate as that drive.
- There is no single standard device that can analyze and interpret distortions (even if there were, it would be useless due to the above points).
- Most of the distortions analyzed are not related to the drive.
- There is no clear standardized method for examining W&F (not related to test record)
- To compare two turntables, it would be necessary to use the same record, the same tonearm, and the same cartridge. An absurd measurement solution.
We want to measure the drive, but why is it so important? Why are rotational consistency and accuracy so crucial?
Rotational accuracy allows for the precise reproduction of recorded frequencies. For instance, if a record has a recorded sound of A = 440Hz, we must play the record at exactly 33.3 or 45.11 RPM to achieve the same A = 440 Hz sound. If the platter speed is lower or higher, we will automatically get a different sound. For example, reducing the speed to 32.724 instead of 33.3 RPM will result in 432Hz. This is not a different pitch, but it is noticeable! (lower is G# = 415Hz, btw 432Hz is part of another theory altogether).
The consistency of rotations, or stability, is crucial to maintaining a constant sound. If the platter speed varies over time and the amplitude of the change is significant, we will hear a wavering sound (the aforementioned WOW and Flutter).
For example, if the speed slowly fluctuates between 33.42 and 33.26 RPM (I have heard turntable working like that), it causes a change in tone between 441 and 439 Hz. It’s just 2 Hz, but I suggest using a simple frequency generator on a cell phone and switching between these frequencies – the difference is quite noticeable. A turntable with such deviations can only serve as furniture or decoration.
In a drive, we aim for the speed to be accurate and for deviations to be as minimal as possible.
So how can we check if our drive is okay?
We need a method based on a single hardware, system, and software platform. A method that does not analyze sound but the drive itself (to eliminate the imperfections of the record and tonearm). A method fit for modern times.
It so happens that such tools have already been developed. The civilian version, designed for every user, is available as an application for modern cell phones. The professional version, created for a single purpose, is called SHAKNSPIN.
I will write about measurement tools and results next time. Stay tuned!