20/06/2021
THIS STUDY BEGAN as a general investigation into forms of SLEWing induced distortion in audio sistems in general, and in IC op amps used in audio electronics in particular. Since so very much has been written in the past few years on transient inter modulation distortion (TIM)(slewing induced distortion) in audio amplifiers most particularly the power amplifier my original object was to seek some answers to which I could attach numbers and correlate these with what I heard.
Many of these writings damn IC op amps (used in every audio equipment) as the bane of the quality sound we all seek and treasure. On the face of some of it, one should dismiss the use of IC op amps in audio signal path as something abhorrent, to be avoided at all costs. And indeed, some of the correspondence I receive doesn't just suggest this, it virtually demands it. I'm sure we have all read more than one equipment review which has mentioned “IC“ (chip) or “transistor“ sound, the harsh, hard, gritty stuff that grates the sensitives.
But, if we sit back and reflect on the overall recording-to-reproduction system (of which our own end is only a part), we can see some obvious inconsistencies.We all know a recorded signal goes through many, many IC op amps(chips) before it reaches our ears and most of them are beyond our control. Consider an obviously well recorded example of today's releases and think we can all agree the sound can be very good. Many mixing console manufacturers use design concepts based largely on IC op amps, of either IC or modular variety. Some have excellent track records, while others do not. So great a number of companies use IC op amps in their products that the sheer numbers as well as the design differences (even if all details were available) would prevent us pinpointing which of these sound good and which sound bad.
Many people evidently see no reason to get excited over the SLEW RATE flap; and simply do not believe it is a major audible defect. I can recall one design engineer (who claimed to be an audiophile)who said any distortion above 10Khz was not worth worrying over, as it was by definition inaudible. This is naive optimism.
Consider the presence of two high level, high frequency tones with a close frequency spacing (etc. 10Khz and 11Khz).Their frequency inter modulation (1khz) product pops out down in the bass or mid (in this example) frequency region, and is HIGHLY audible.
And this is exactly the way slewing induced distortion works on two-tone inter modulation tests producing strong low/mid frequency inter modulation components.You should also consider brief high frequency transients as well as tones. If the slewing rate of an audio process is pushed (not even exceeded, necessarily) even momentarily, intermodulation will occur and will probably be audible.It can also occur (indeed, is most likely) with high level supersonic signals (over audio range 20Khz) which will cross-modulate down into the audible region as the answer on difference between 44.1khz 48khz or 96khz mix down of our music that is better higher sampling rate..
Sometimes yes but sometimes no, but we will talk later.
Wellcome to our BPM Audio Concept WEB Page.
Nikola Fuchkar
https://www.facebook.com/nikola.fuchkar
