Despite many noise complaints about it, the Te Rere Hau farm, east of Palmerston North, complies with noise standards and a planned extension will also comply, according to NZ Windfarms.

The company wants to build 56 more turbines on the eastern side of the Tararua Ranges, but is running into opposition from neighbours annoyed about noise.

Noise expert for NZ Windfarms Malcolm Hunt said at a hearing on the proposed extension yesterday that wind turbines could be heard, but that did not mean the noise was unacceptable.

"The fact that something can be heard does not mean it is not complying with the applicable noise standards," he said.

Mr Hunt said he did not believe that noise descriptions such as "wump wump wump" and "thumping" accurately reflected the sound impact objectively.

There was no evidence that audible sound from Te Rere Hau was significant beyond the wind farm boundary, he said.

NZ Windfarms has investigated whether the sound from the wind farm has a tonal component, which could make the noise more annoying to people. Tonal noise is considered to have a pitch.

Acoustics expert for NZ Windfarms Miklin Halstead said while tonal noise had been detected near the wind farm, the level at nearby properties did not cross the threshold that would warrant an adjustment for that.

However, Tararua District Council noise consultant Nigel Lloyd argued tonal noise could be better assessed near the turbines.

Mr Halstead said an examination of complaints showed that they occurred in a range of wind speeds and wind directions.

"The conditions during which complaints have occurred are not necessarily the loudest periods, but include quieter periods where wind farm sound is more exposed."

The policing of cumulative noise was again raised at the hearing yesterday as it was unclear what would happen if consents were granted for both the Te Rere Hau extension and the planned 121-turbine Turitea farm nearby.

NZ Windfarms lawyer Mike Holm said both wind farms would be required to meet noise standards.

If overall noise became a compliance issue, Turitea might have to cut the power output of some of its turbines or relocate them, he said.