A turbocharger, comprising: a turbine including a turbine housing; a compressor assembly comprising a compressor housing and a compressor wheel mounted in the compressor housing and connected to a rotatable shaft for rotation therewith, the compressor wheel having blades and defining an inducer portion, the compressor housing comprising a first housing portion and a second housing portion, the first housing portion including an air inlet wall circumscribing an air inlet for the compressor wheel, the second housing portion defining a tip shroud for the compressor wheel and defining a volute for receiving compressed air from the compressor wheel, the compressor housing upstream of the compressor wheel defining an annular space located radially outward of the air inlet, an axial extent of the annular space being bounded between a radially extending upstream wall which is part of the first housing portion and a radially extending downstream wall which is part of the second housing portion, a radially innermost extremity of the annular space being open to the air inlet; and an inlet-adjustment mechanism disposed in the annular space and adjustable between an open position and a closed position, the inlet-adjustment mechanism being movable radially inwardly from the annular space into the air inlet into the closed position so as to create an orifice having a reduced diameter relative to a nominal diameter of the air inlet; characterized in that the first housing portion defines a first opening that leads into a first quarter-wave resonator cavity defined within the first housing portion, the first opening is defined in the radially extending upstream wall and the air inlet wall does not define any openings into the first quarter-wave resonator cavity. a turbine including a turbine housing; a compressor assembly comprising a compressor housing and a compressor wheel mounted in the compressor housing and connected to a rotatable shaft for rotation therewith, the compressor wheel having blades and defining an inducer portion, the compressor housing comprising a first housing portion and a second housing portion, the first housing portion including an air inlet wall circumscribing an air inlet for the compressor wheel, the second housing portion defining a tip shroud for the compressor wheel and defining a volute for receiving compressed air from the compressor wheel, the compressor housing upstream of the compressor wheel defining an annular space located radially outward of the air inlet, an axial extent of the annular space being bounded between a radially extending upstream wall which is part of the first housing portion and a radially extending downstream wall which is part of the second housing portion, a radially innermost extremity of the annular space being open to the air inlet; and an inlet-adjustment mechanism disposed in the annular space and adjustable between an open position and a closed position, the inlet-adjustment mechanism being movable radially inwardly from the annular space into the air inlet into the closed position so as to create an orifice having a reduced diameter relative to a nominal diameter of the air inlet; characterized in that the first housing portion defines a first opening that leads into a first quarter-wave resonator cavity defined within the first housing portion, the first opening is defined in the radially extending upstream wall and the air inlet wall does not define any openings into the first quarter-wave resonator cavity.