Use distortion or overdrive to add texture and roughen the sound instead of just boosting the highs, avoiding being too "fizzy." Add reverb with a long decay time and a little pre-delay to create a sense of space, combined with modulated reverb to add a unique touch to the sound. Use tape delay with modulation to create a soft, “washy” sound. Finally, instead of cutting the low end completely at 400Hz, try lowering it to around 200-250Hz to retain some depth, and cutting it gently around 2-4kHz to avoid sounding too sharp.
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