Are Allpasses Really Colorless?

• Allpass impulse response only ``colorless'' when extremely short (less than 10 ms or so).
• Long allpass impulse responses sound like feedback comb-filters
• The difference between an allpass and feedback-comb-filter impulse response is one echo!
  
  (a) $H(z) = \frac{0.7+z^{-7}}{1+0.7z^{-7}}$ (b) $H(z) = \frac{1}{1+0.7z^{-7}}$
• Steady-state tones (sinusoids) really do see the same gain at every frequency in an allpass, while a comb filter has widely varying gains.