I think he favors a toothed belt
In high-end turntables, the type of drive belt used plays a significant role in overall performance and sound quality. Among the most common belt types—round belts, flat belts, and toothed (or timing) belts—flat belts are generally considered the best and most widely used solution in high-end designs.
Flat belts offer an ideal balance between efficient torque transmission and mechanical isolation. Their broad surface ensures smooth and stable contact with the motor and platter, minimizing wow and flutter. This leads to excellent speed stability and low noise, which are crucial for audiophile-grade playback. As a result, many respected high-end brands (not even at ASR, but usually) such as Clearaudio, Linn, and Rega (in some models) use flat belts in their belt-drive systems.
Round belts, by contrast, are more commonly found in mid-range or vintage turntables. They are simpler and less expensive but tend to have issues with uniform tension and speed consistency, which makes them less suitable for top-tier performance.
Toothed belts, or timing belts, ensure very precise power transmission without any slippage. However, the mechanical interaction of the teeth can introduce microvibrations, making them less desirable for high-end audio where vibration isolation is critical. For this reason, they are rarely used in high-end turntables, though some specialized systems may incorporate them in hybrid configurations.
In summary, flat belts are (or were?) the most common and preferred choice in high-end turntable engineering due to their superior balance of smooth operation, low noise, and precise speed control.
I haven't had a record player myself for a long time, but I don't think that should have changed.