To the best of my knowledge, cabins are never pressurized before takeoff. This is a safety issue as it would inhibit door opening as the pressure would make them impossible to open.

Depending on aircraft, the aircraft might be kept at either:

• At a constant pressure difference, i.e. the cabin altitude increases evenly up to cruise altitude. This would indeed mean that the moment it takes off it starts to build up a pressure in relation to takeoff. This means that the pressure difference is perceived as gradual.
• At a fixed minimum pressure, i.e. the valve just closes at (for instance) 2000m and then maintains 2000m altitude all the way up, just building an increasing pressure differential.

The former is more common since it's nicer. This would also explain why you perceived a change even at high altitude.

To the best of my knowledge, cabins are never pressurized before takeoff. This is a safety issue as it would inhibit door opening. The pressure would make them impossible to open.

Depending on aircraft, the aircraft might be kept at either:

• At a constant pressure difference, i.e. the cabin altitude increases evenly up to cruise altitude. This would indeed mean that the moment it takes off it starts to build up a pressure in relation to takeoff. This means that the pressure difference is perceived as gradual.
• At a fixed minimum pressure, i.e. the valve just closes at (for instance) 2000m and then maintains 2000m altitude all the way up, just building an increasing pressure differential.

Both methods have to take into account the landing altitude, since you don't want to land the aircraft pressurized.

The former is more common since it's nicer. This would also explain why you perceived a change even at high altitude.

To the best of my knowledge, cabins are never pressurized before takeoff. This is a safety issue as it would inhibit door opening as the pressure would make them impossible to open.

Depending on aircraft, the aircraft might be kept at either:

• At a constant pressure difference, i.e. the cabin altitude increases evenly up to cruise altitude. This would indeed mean that the moment it takes off it starts to build up a pressure in relation to takeoff. This means that the pressure difference is perceived as gradual.
• At a fixed minimum pressure, i.e. the valve just closes at 2000m and then maintains 2000m equivalent altitude all the way up.

The former is more common since it's nicer. This would also explain why you perceived a change even at high altitude.

To the best of my knowledge, cabins are never pressurized before takeoff. This is a safety issue as it would inhibit door opening as the pressure would make them impossible to open.

Depending on aircraft, the aircraft might be kept at either:

• At a constant pressure difference, i.e. the cabin altitude increases evenly up to cruise altitude. This would indeed mean that the moment it takes off it starts to build up a pressure in relation to takeoff. This means that the pressure difference is perceived as gradual.
• At a fixed minimum pressure, i.e. the valve just closes at (for instance) 2000m and then maintains 2000m altitude all the way up, just building an increasing pressure differential.

The former is more common since it's nicer. This would also explain why you perceived a change even at high altitude.