Handcrafted Tone
Well-known member
I've been thinking about the Little Labs I B P , and wondering what makes it tick.
This is the block diagram from the IBP manual:
Researching all pass filters I found this:
a single-pole, single-zero all-pass filter passes all frequency components with constant gain and a phase shift which may be adjusted by the placement of a pole. Taking Z0 near the unit circle causes most of the phase shift to be concentrated near the frequency where the pole is located. Taking the pole further away causes the delay to be spread over more frequencies. Complicated phase shifts or group delays may be built up by cascading several single-pole filters.
I vaguely understand this statement, but I'm clueless on how to use the ALL PASS in the IBP block diagram. Is variable shift possible inside the all pass circuit, or is it from stacking multiple all pass filters together? I would be happy with a stepped phase switch, with -90, -45, 0 , 45, 90, and 180 degree adjustment. Would that mean 5 different all pass filters? Is that even possible?
Some more info I found on the web:
The networks themselves are virtually identical, with only the position of the resistor and capacitor (R1 and C1) changed. This effectively reverses the frequency at which there is no phase shift - in this case we would arbitrarily select around 10Hz as the 'reference' frequency. At such a low frequency, the capacitor has virtually no effect with either network, and the circuits can be considered to be (almost) conventional inverting and non-inverting opamp circuits
Thanks in advance!
This is the block diagram from the IBP manual:
Researching all pass filters I found this:
a single-pole, single-zero all-pass filter passes all frequency components with constant gain and a phase shift which may be adjusted by the placement of a pole. Taking Z0 near the unit circle causes most of the phase shift to be concentrated near the frequency where the pole is located. Taking the pole further away causes the delay to be spread over more frequencies. Complicated phase shifts or group delays may be built up by cascading several single-pole filters.
I vaguely understand this statement, but I'm clueless on how to use the ALL PASS in the IBP block diagram. Is variable shift possible inside the all pass circuit, or is it from stacking multiple all pass filters together? I would be happy with a stepped phase switch, with -90, -45, 0 , 45, 90, and 180 degree adjustment. Would that mean 5 different all pass filters? Is that even possible?
Some more info I found on the web:
The networks themselves are virtually identical, with only the position of the resistor and capacitor (R1 and C1) changed. This effectively reverses the frequency at which there is no phase shift - in this case we would arbitrarily select around 10Hz as the 'reference' frequency. At such a low frequency, the capacitor has virtually no effect with either network, and the circuits can be considered to be (almost) conventional inverting and non-inverting opamp circuits
Thanks in advance!
