How to check if your FLAC files are really lossless

Lossless audio is a wonderful thing! By using lossless audio you know that the source material is not the weak link. But have you ever thought “are my FLAC files true lossless audio, or were they upconverted”? Some stores have been caught selling audio of lesser quality packaged as FLAC.

The good news is that it’s easy to find out!

We are going to use a spectrum analyzer to inspect the true bitrate of the files. A good and popular choice for this is Spek (, which is available for Windows, Linux and macOS.

When we open a file in Spek, we will see a spectrum display of the entire file. Depending on the frequency at which it cuts off, we can determine the bitrate.

Generally these are the numbers to go by:

  • 11 kHz = 64 kbps
  • 16 kHz = 128 kbps
  • 19 kHz = 192 kbps
  • 20 kHz = 320 kbps

If there is no cutoff, the file is most likely lossless.

Let’s look at some examples. Here I’m looking at a legally acquired track. I have imported it for personal use from a CD I bought, but I also bought the official download in 96 kHz, 24-bit so I am also going to compare to that.

First we can see a spectrum we really don’t want to see. This is what the 44 kHz, 16-bit file looks like after being converted to a 128 kbps MP3 and then converted to FLAC. There is a sharp cutoff at 16 kHz. This audio is not lossless.

Next let’s take a look at a 320 kbps MP3 converted back to FLAC. This time it cuts off at 20 kHz, consistent with the table above for a 320 kbps file.

This below is what a 44 kHz, 16-bit file should look like. It goes all the way up to 22 kHz with no cutoff below.

Now, let’s look at something with a bit more headroom. This is the 96 kHz, 24-bit file. It’s fairly obvious that this file goes well beyond the hearable range, which tops out at about 20 kHz. There is great debate on whether or not anything above that actually contributes anything to the experience or not. I know I can’t tell a 96/24 and 44/16 file apart.

If you want to check a lot of files this method can be a little bit tedious, but fortunately there is a tool for that too. I don’t know if it can be fully trusted, I like to see the spectrum myself, but it saves a lot of time. Lossless Audio Checker (, available for Windows (GUI), Linux and macOS (both command line only). Here’s what it looks like when testing it on my four files used earlier with Spek.

Now all you have to do is try these tools with your files.