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AB_LM (AB Loudness Match)

Product description

AB_LM is a gain control which enables level matched and sample accurate AB comparison of FX chains.

We at TBProAudio found us very often in mixing or mastering situations where we need to quickly identify the contribution of a certain plugin (FX) or even a complex FX chain to the sound.

Most DAWs can easily enable/disable (AB) single plug-in or even whole FX chains, but in most case there is an audible loudness difference between both cases. In order to compare the impact of a plugin chain objectively the loudness of the incoming signal should match with the loudness of outgoing signal.

Comparing the plugin effect at equal loudness levels avoids the "louder is better" - pitfall.


Mode & Link Channel

Sets the mode of the plugin, either Sender or Receiver and the link channel for the communication. Sender is placed before the plugin(s) which should be AB level matched, Receiver is inserted after. Use the "L"-button (auto) to quickly set next highest (free) sender/receiver channel. In addition AB_LM makes suggestions for channel auto link, which may work depending on DAW/plug-in type.

Latency Compensation

Some plug-in add latency to the plugin chain. For a sample-exact AB loudness comparison audio streams need to be synchronized. This can be done automatically (just press PDC button and wait 1-2 seconds) or manually by entering the latency value (in samples).

Pre-FX Loudness

This meter shows the current and maximum loudness of the audio stream just before the plugin(s). Many plug-in work best at a certain loudness level (e.g. -18 dBFS)

Post-FX Gain

This meter shows the loudness difference of pre and post-FX signal. The match button lets you set the additional post-FX gain (match mode "manual") based on current loudness difference. Match mode "Auto" does this automatically.

Match Modes

AB-LM lets you match the loudness either manually, or automatically. The match gain is added after FX chain. If "inverse" is enabled match gain is added before FX chain. The mode "Gain Stage" works differently: The additional FX drive gain is just removed from the audio stream right after the FX chain for "pure" gain staging purposes. 

Snapshot Slots

AB_LM provides 4 snapshot slots to store and recall settings for FX drive and Post-FX gain. So you can test your plugin chain with different gain levels, all loudness matched.

FX Drive

This parameter adjusts the additional pre-FX gain.

AB Switch

This button lets you seamless switch between pre and pre-FX audio signal.

Pre-FX Gain

This meter shows how close the loudness of the incoming signal is matched with a certain reference level. Many engineers work with loudness calibrated audio systems.


Demo version versus Registered version

In demo mode (without registering) the plugin mutes audio every 90 seconds for a short period. This could be circumvented by clicking on the "AB_LM" logo within 90 seconds.


Please download AB_LM here.

System Requirements




Please order AB_LM registration key here.




Top Mix Tip: Using Reference Tracks - Warren Huart: Produce Like A Pro

DAW gain-staging


- GainStaging: remove PreGain during AB off

- DSP code optimizations

- Gain staging fix: add. PreFXGain compensated
- VU Metering

Fixed PDC bug

Small bug fixes for issues which could cause incorrect measurement after a while

RMS modes changed: RMS->RMS sum, RMS+3->RMS avg

Fixed Pre FX max readout
EBU filter denormal fix

Auto link channel:
works optimal in pairs
new plug in instance: even instance_count => sender, odd instance_count => receiver, next free channel is chosen (does not work for AAX/RTAS)
copy track with linked pairs: sender/receiver pair is re-linked (does not work for AU and AAX/RTAS)
copy plug in: next free channel is chosen

(Attention: Please remove all instances of AB_LM before installing V1.3.0 (incompatible parameter set))
Added auto channel select
Link channels extended to 256
RMS/EBU measurement bug fixed

(Attention: Please remove all instances of AB_LM before installing V1.2.0 (incompatible parameter set))
Adds Measurement Modes EBUR128 ML (400ms) and EBUR128 SL (3000ms)

Small GUI fixes

Inverse gain match switch
Link channels extended to 32

Fixed crackle in auto gain mode during startup

Demo "Stutter" fix

Initial release