“The Square Wave on a scope is a quick way to show problems. This just was that I was repairing an old EAR802 preamp I made in the early 80s. I put in a subsonic filter for those with bad rumble turntables. This is the effect of a simple 3rd order filter that is 3dB down at 16 Hz.
The effect on music is a rhythmic timing effect. That is because the phase at 40 Hz is leading by some 30 degrees, means that the fundamental of say a string bass arrives earlier than the clicky finger part, so you perceive it as a dragging pace. All typical tape recorders suffer severe bass phase coherence and this makes for this slower pace which for many people is attractive but wrong. Other methods such as spectrum graphs or response graphs don’t illustrate this as clearly. It just staggers me how little attention is paid to these details. Disc cutting systems are generally better in this regard. Unfortunately most disc cutting systems have problems with the high frequencies due to the severe 75 microSecond time constant. I in my tape recorders deal with this to make phase shift at low frequencies as small as possible, If I can extend the low end at 15 ips down to about 7 Hz. then I capture a better bass quality. A well set up Ortophon cutting system was minus 3dB at 3 Hz. So bass was limited to the playback arm and cartridge resonance.”