Informer - Detect lossy audio!
Is that CD legit? Are those FLAC
files just recoded MP3s in disguise? Now you know. Informer is a real-time spectrograph with a special purpose: To help detect lossy encoding (such as MP3) in an audio stream. Informer listens to your sound card's wave output and creates a graph that makes lossy compression easily visible.
MP3, and other lossy formats, create conspicuous patterns in tonality. High frequencies may change from frame to frame, or certain frequencies may be omitted, in unusual and artificial-looking shapes. The general rule is look for rectangular or stair-step patterns
in Informer's output, especially between the red and green lines.
Informer is good for finding many types of lossy formats:
- MP3 is visible at all bit rates.
- WMA is visible at all bit rates.
- Musepack is visible at all bit rates.
- Ogg Vorbis is visible at under 300 kbits/sec, but becomes difficult above that.
- MPEG-4 AAC is visible at under 200 kbits/sec, but becomes difficult above that.
The future is lossless. Make sure your stuff really is
How to use
First, set up your PC sound card to record its own wave output. Depending on your sound card or motherboard, this option may be called "Stereo Mix", "Wave", "What U Hear", etc.
Now run Informer, and play a song in any media player, such as Winamp. You should see the analysis of the sound start to scroll by. If not, try selecting a different audio device in the Input → Device menu.
The X axis represents frequency, with 0 Hz on the left, and 24 KHz on the right. The red line is 16KHz (the limit for many MP3s); the green line is 22.05 KHz (the limit for CDs). The Y axis represents time.
Test it out by playing some MP3s, and then some lossless tracks. Things you should watch out for:
- Rectangular, jagged, or stair-step patterns are caused by abrupt changes in the stream's frequency response, usually coinciding with frame boundaries in lossy formats such as MP3.
- The patterns may be worst between the red line (16 KHz) and green line (22.05 KHz).
- If everything to the right of the red line (16 KHz) is dark, it's probably lossy.
- The patterns may also be more apparent if you switch to a different channel (Side, Left or Right).
- If you see a mirror image, either the player or sound card is resampling improperly. Try YouTube for an example.
Hold the left mouse button anywhere in the window to freeze the output momentarily.
- Selects which sound device to use for recording. Any device which supports DirectSound can be used. Under Windows Vista or later, native devices (marked as [Vista]) should work best.
- Sample Rate
- Selects the sample rate. 48 KHz is the default. Some devices may be locked to a specific sample rate, in which case you won't be able to change it.
- Center: Examine the center (L+R) signal.
- Side: Examine the side (L-R) signal.
- Left: Examine the left (L) signal.
- Right: Examine the right (R) signal.
- Roundoff Error: Computes tonality and then enhances the roundoff error. This is the mode which is most useful for detecting lossy audio, and is the default.
- Tonality: Measures the predictability of magnitude and phase at each frequency bin.
- Amplitude (dB): Amplitude of each frequency bin in decibels.
- Select which color palette to use for the spectrograph.
- Enable or disable scrolling of the spectrograph.
- Show frequency tooltip
- Enable or disable the frequency tooltip.
- Actual Width
- Snap the window to the actual size of the analysis (1 pixel = 1 frequency bin).
- Use this menu to adjust the process priority. If you're running many other CPU-intensive programs, you might find Informer runs more smoothly set to Above Normal or High. As with any program, be careful when increasing the priority.
The application failed to initialize properly (0xc0000135).
This error message will appear if you don't have the .NET Framework installed. You can get this from Windows Update.
The window fills with noise when there's no sound.
This is normal and is attributable to roundoff error, especially when the "Roundoff Error" algorithm is selected. As soon as you play a sound with sufficient volume, the spectrograph should lock on to the relevant frequencies again. If you can't get it to work, try changing the input device from the Input menu.
The window doesn't scroll at all when there's no sound.
This is normal under Windows Vista or later.
- Windows 2000, XP, Vista or later.
- .NET Framework 2.0. If you don't have this, you can get it via Microsoft Update.
- The latest version of DirectX.
- A fairly fast CPU (1 GHz recommended).
- A sound card or motherboard that can record via DirectSound.
Informer is distributed under the terms of the GNU General Public License Version 3
Informer makes use of the excellent FFTW
library by Matteo Frigo and Steven G. Johnson.
Informer also makes use of the research notes of Bosse Lincoln: An Experimental High Fidelity Perceptual Audio Coder