A Perth man who admitted sexually abusing a young girl during group sex sessions involving up to four adults, including her mother, has been sentenced to 21 years jail.

Key points: Tracey Coulter joined in the abuse of the eight-year-old with her mother and stepfather

Tracey Coulter joined in the abuse of the eight-year-old with her mother and stepfather Judge Bruce Goetze described the abuse as "depraved and perverted"

Judge Bruce Goetze described the abuse as "depraved and perverted" Coulter was sentenced to 21 years jail and is eligible for parole in January 2037

Tracey Coulter, 57, pleaded guilty to a string of charges including persistent sexual conduct with a child, sexual penetration of a child and making an indecent recording.

The District Court was told some of the abuse was recorded, and in two separate video clips handed into police the then eight-year-old girl was shown being abused "simultaneously or in quick succession" by three adults, including her mother and stepfather.

There was also what was described by Judge Bruce Goetze as "sexual banter" and at one point the mother was heard to say "she's definitely her mother's daughter".

The other abuse happened about a year earlier on three occasions when the girl was six or seven years old, and involved her being abused after the adults and her watched pornographic movies involving children.

The court was told that each time the girl was also given a pipe to smoke that contained a stupefying substance and in one instance she was made to record some of the sexual activity between the adults, again including her mother.

Coulter was charged after police raided properties in Perth and regional WA. ( Supplied: WA Police )

'This was a birthday surprise'

One of the sex sessions happened around the girl's seventh birthday, and the court heard one of the adults told her beforehand that "this was a birthday surprise" for her.

Judge Goetze said he had read a victim impact statement from the girl, who was now aged 12, in which she said she sometimes felt what happened was her fault.

"My comment to her, and she must understand, that this is not her fault, she has done nothing wrong," he said.

"She was at all times … a young and innocent child."

Judge Goetze described the abuse as "depraved and perverted", saying it had corrupted a young child who in the video recording appeared "fully compliant" with the offences that were being committed against her.

"It had been normalised for her," he said.

Judge Goetze said one of the aggravating factors in the case was that the abuse was recorded.

"Why it was filmed, no one knows," he said.

Coulter will be first eligible for parole in January 2037. ( ABC News: David Weber )

"While it wasn't made to be disseminated, it was disseminated and this child will live with the fear that in some future time … it may be shown, she may be recognised and she'll have these offences drawn out again."

He also said the girl, because of her young age, may not yet fully understand the effect of "the degradation and humiliation" that had been inflicted on her, something he said she may not realise until she was much older.

Videos are 'indefensible': judge

Coulter had claimed to police he was under the influence of methylamphetamine and had no memory of the offences, but that was not accepted by Judge Goetze who described the videos as "indefensible".

"This was perverted conduct, borne out of a warped sense of desire and carnal lust … without any regard for this young girl."

"She has been totally corrupted."

"This is depraved and despicable conduct. The complete defilement of an eight-year-old girl."

In deciding what sentence to impose, Judge Goetze took into account Coulter's early pleas of guilty which he said had spared the girl from having to give evidence at a trial.

Coulter will have to serve 19 years before he can be released.

With time already served, he will first be eligible for release on parole in January 2037.