Earlier this year, Spotify placed restrictions on its free version, slashing the amount of times a track can be played and the total amount of music users can listen to without paying, in order to attract more users to sign up for its ad-free pay service.
The premium version allows users to listen to their playlists offline and to access their music through their mobile phones. It also boasts a higher sound quality at 320 kbps.
But on Friday Swedish trade magazine Computer Sweden reported that when a holder of a premium account from the American blog Spotifyclassical checked the sound quality of 115 random tracks, only a third maintained the promised 320 kbps.
Several more random checks have been carried out, claimed the paper, showing similar results.
However, on Spotify's website the company declares that "not all tracks are currently available in high bitrate" and thus appearing to meet marketing regulations.
The bone of legal contention appears to be a comment made by a Spotify support employee on an official support forum last year regarding the extent of the catalogue which was available at 320 kilobit/second (kbps).
“We're somewhere in the 60% range of the entire catalogue and considering that we convert based on popularity, that covers most of what people listen too,” the employee said at the time.
According to legal expert Marek Andersson at the Swedish Consumer Agency (Konsumentverket), this claim could constitute false marketing.
“Someone could have read the answer and based their decision to join on that statement. Then it could fall under marketing law,” Andersson told Computer Sweden.
He stressed though that a more extensive investigation into the matter would be necessary in order to ascertain if the company is in breach of marketing laws or not.
Johan Chandokar, a sound engineer from Sveriges Radio, told the Sydsvenskan daily that the average Spotify-user probably wouldn't notice much difference if the sound is streamed at 160 or 320 kbps.
“As it is right now it is acceptable and fully usable,” he said to the paper.
However, enthusiasts of jazz or classical music might react to the different qualities, as those sounds are more complex, he said.
At Spotify they say that all music streamed through the service is of high quality (160 kbps) and that they have a very broad catalogue of over 15 million tracks.
“All tracks are not currently available in high bitrate (320 kbps) for our Premium users, which we make clear on our website, but we are working very hard to transcode the remaining tracks, as quickly as possible,” the company said in a statement.
As their catalogue increases at an average of 10,000 new tracks each day, they say it is an ongoing task, but the matter is treated as a high priority, according to the company.
Spotify launched in the United States last week with the ambitious goal of attracting 50 million US users within a year.
Spotify has 10 million users in Europe and is offering three options in the United States: a free, advertising-supported streaming service, an ad-free $4.99 a month plan for computer listening and a $9.99 a month plan allowing subscribers to download as many tracks as they want to an iPhone or Android device.