Ferrari driver Sebastian Vettel believes Formula One engines are still not as loud as they should be, though the four-time world champion was happy with the improvement made from last year.
Teams have introduced a modified exhaust system to try to boost the engine sound after widespread complaints the cars have been too quiet since the switch to a 1.6-litre V6 turbo from V8 engines in 2014.
While Vettel admitted the new exhaust system saw a slight increase in sound, he believes the engines are still far from what they should be.
"I can say it is nice to have a bit more sound coming back," the German told reporters.
"It is still not as loud as it could or should be but it is a lot better than it was, now sounds a bit more like Formula One."
Vettel continued his impressive pre-season form after topping the timesheets once again on the second day of testing in Barcelona on Tuesday.
"We worked on a lot of things, it's a brand new car, which means there are a lot of new bits and things are in a different place," he said.
"We tried to understand how the car reacts, obviously we had an idea and certain expectation, but when you run the car on track it is always a bit different, you are then dealing with temperatures, cooling etc.
"Sometimes you have to stop a bit longer than necessary or than you really want, just to check, other times the driver goes off track, like I did this morning.
"But these things happen. Overall we are happy, but we know that we need now a lot of mileage, so there is a lot of work ahead of us."
Vettel clocked 126 laps around the Circuit de Barcelona-Catalunya, followed on the timesheet by Red Bull's Daniel Ricciardo and Force India's Sergio Perez.