Time stretching using FMOD_DSP_PITCHSHIFT_PITCH and setFrequency make the sound unclear and its volume lower

I used FMOD_DSP_PITCHSHIFT_PITCH and set frequency together to lower speed of the song without changing pitch.
if I don’t use FMOD_DSP_PITCHSHIFT_PITCH the sound is clear, but when use FMOD_DSP_PITCHSHIFT_PITCH the sound becomes unclear
Also I used dsp Info and saw that the vu meter shows lower values when FMOD_DSP_PITCHSHIFT_PITCH is used.
How is that and how I can overcome this issue?

Have you tried increasing FMOD_DSP_PITCHSHIFT_FFTSIZE above the default to reduce “smearing,” as described in the FMOD-DSP_PITCHSHIFT documentation?

What’s the sample rate of the audio file you’re lowering the play speed of?

Yes, I have set it to 4096, better quality longer delay but still lower volume
sample rate is 44100

Is there any updates? what should I do to prevent the issue!

I’ve added this issue to our bug tracker, but we have not yet released a fix.

If the change is volume is perceptible and a problem for your game, you should be able to compensate for it by boosting the volume.

It is a problem and it is perceptible! but the problem is not just the volume, the sound clearance reduction is the main problem.

I’m sorry, but I’m not sure I understand. What is “sound clearance reduction?”

I think he means the sound quality is the main problem

Assuming that you do mean the reduction in sound quality, l3enQ, there is currently no workaround for that issue.

yep, I mean kind of sound quality reduction. it is like the bass is killed somehow
However I think the problem is with pitch shifting algorithm, and I am seeking for another one to develop it with custom dsp.
Although I can find a time stretching algorithm, but it can not be developed by custom dsp, right? what is the best way to develop such things?

You can find information on developing and using custom DSPs for FMOD Studio here, here, and here.