Murder victim Leon Davis died after an incident in Thornhill Road, Handsworth
A "quiet and peaceful" father-of-four was stabbed to death by his mentally-ill neighbour in a "ferocious" street attack.
Paranoid schizophrenic Adum Osman killed Leon Davis with a kitchen knife before calmly walking off to buy cigarettes.
Birmingham Crown Court heard the Sudanese refugee had convinced himself that the 55-year-old victim was bombarding him with loud music.
But Judge Melbourne Inman QC branded Osman "deluded" and said his complaints about Mr Davis were "unjustified".
The 36-year-old warehouseman was sent to a secure hospital without a time limit after admitting manslaughter on the grounds of diminished responsibility.
The judge told Osman: "On January 31 you savagely attacked and killed Leon Davis in the street.
"It was as senseless as it was violent.
"Mr Davis was a quiet and peaceful man who lead a quiet and happy life.
"No-one saw the attack start.
"This was, however, a residential area.
"Within moments a number of people were confronted with the terrifying picture of you repeatedly and ferociously stabbing Mr Davis as he lay helpless on the floor.
"You then walked calmly to a local shop to buy cigarettes."
The court heard Mr Davis, a carpenter and cabinet maker, lived with his step-father in a flat below Osman in Thornhill Road, Handsworth.
The judge said the killer developed "deluded" beliefs about the victim last November and December and made unjustified complaints to the city council and police.
He went on: "The police were sufficiently concerned about your behaviour that an officer tried to find out whether you had any previous mental health care but it did not appear that you had.
"On that Friday morning you went out armed with a substantial kitchen knife and when you saw Mr Davis in the road you attacked him."
The judge said Osman's responsibility for his actions was substantially reduced as a result of his mental illness.
But he went on: "You are nevertheless a very dangerous man when your illness is not properly treated."
Deborah Gould, prosecuting, said both Mr Davis and his stepfather had health problems.
Osman first made a complaint to a housing association on November 13 claiming they were keeping him awake by playing loud music and talking loudly.
A series of complaints followed but Miss Gould said a police investigation revealed nothing antisocial about their behaviour and they led "a very quiet life of simple routine".
She said witnesses saw Osman crouching over Mr Davis in Thornhill Road on the day of the attack.
Miss Gould went on: "The defendant then drew his right arm back and revealed a large knife that had come from the stomach of Mr Davis."
She said police arrested Osman in a nearby shop and he was then detained under the Mental Health Act.