Feedback Compressor II – Manual
Contents
1. M 12 Enduser licen e acreeMne N PT Om 12 a Thank you for choosing a Tokyo Dawn Labs product CONCEPT The TDR Feedback Compressor Il is a major design update of its critically acclaimed predecessor The compressor is dedicated to the highest fidelity stereo program 2 buss compression but shines equally in classic mixing tasks Most modern compressors analyze the input signal to control gain reduction This is known as a feed forward topology The TDR Feedback Compressor II however analyzes the output This approach delivers unobtrusive and highly musical compression characteristics which mean the compressor is able to handle complex signals with ease more about this in the Feed back compression chapter SIDE CHAIN THRESHOLD PEAK SOFT PEAK RATIO MAKEUP HP FILTER CREST KNEE RATIO 2 LIM SLOPE 6d8 Oct Q gt FREQUENCY 13 0 dB DRY MIX ATTACK RELEASE PEAK RELEASE RMS AA N z SIDE CHAIN v r v v STEREO DIFF PRECISE OUT GAIN 100 0 10 ms 150 ms 250 ms 0 0 dB The TDR Feedback Compressor II takes this traditional compression topology to new heights as a state of the art dynamics processor combining an unusual and highly flexible yet intuitive control scheme The compressor has been carefully tuned for intuitive and musical operation for almost every situation No compromises have been made in order2. The transfer function display covers a range between OdB and 65dB The main threshold is indicated by the red line The soft knee region appears in dark red always below the main threshold line The blue bar on the right shows the current gain reduction applied to the signal An additional slowly decaying dark blue bar shows the maximum reduction over a bigger time frame The scale range can be switched by clicking the scale or meter area left click to increase range right click to decrease A red warning marker appears at the bottom of the reduction bar in case the reduction amount exceeds the current scale PRECISE ECO MODES This switch allows the user to select a more efficient processing mode to save a few CPU cycles ic for less critical situations This ECO mode is not meant as creative parameter No matter what you mean to hear the process is the same just at lower quality DELTA This allows the user to listen to the difference between the original and compressed signals This is best described as what the compressors actually does and is very useful to get a better understanding how different settings affect the original signal BYPASS Bypasses the whole processor Processor latency is accurately compensated and the actual processing is never interrupted gapless to enable better comparisons 11 CONTROLS AND DISPLAYS All controls within the plugin feature acceleration This is to say fast movem
3. important to have an idea of the things going on under the hood The compressor is designed to handle complex program material To achieve this the compressor runs two distinct and separate detection circuits in parallel A Peak Path The peak detection compression path follows the true audio waveform closely B RMS Path The RMS path reacts to overall energy levels similar to human hearing and ignores instant events It s best imagined as a very slow and smooth compressor that handles the constant or steady state parts of the signal The path generating the highest reduction takes control of the whole compression action Absolute input The approach offers the advantages of peak compression combined with the advantages of RMS compression Furthermore the RMS path negates the disadvantages of the peak path and vice versa It design guarantees a very stable a sound image and low compression artifacts over a wide range of material and settings Peak over threshold RMS over threshold aA Peak with attack and fast release RMS with attack and slow release Image is a rought approximation Attack set to zero in thia example THRESHOLD PEAK CREST SOFT KNEE AND RATIO THRESHOLD PEAK SOFT RATIO Threshold defines the level above which the compressor CREST KNEE RATIO Yos Lint 2 begins to compress the signal The lower the threshold the deeper the grab and the more compression Pe
4. to achieve the highest possible quality of dynamic control We want to emphasize the fact that the processor neither tries to emulate any previously available device nor does it follow popular trends like virtual analogue circuit modeling or similar buzz words This is a proud digital processor made with an immense amount of love and care Beside the inherent feed back behavior the processor comes with an array of unusual features which offer great flexibility The most notable are probably the unusual two stage release timing controls the Peak Crest control scheme a generous transfer function display and metering section as well as mastering optimized sidechain filters and stereo link options The following pages cover the advanced features of the processor it is a prerequisite that the reader is accustomed to dynamics processors and their uses FEED BACK COMPRESSION Dynamic range compression can be accomplished in several ways The most straight forward approach is to detect the input level and use that signal to control an amplifier Level Detection This kind of control structure is called feed forward The device analyzes the input and reduces gain accordingly Most modern compressors are built this way A different behavior can be achieved by feeding the detector with the output of the compressor Level Detection In this case the detector envelope follower detects the level at th
5. TOKYO DAWN LABS Feedback Compressor Il Manual Product version 2 0 0 Revision 1 7 last update 03 16 2013 Editors Fabien Schivre Dax Lini re Puzzle Factory CONTENTS c PH 4 Feedback 5 Pr cision Aliasing the solution uico cis Ea cU FM ine nes SUUS 6 OI NS ET m rm 7 Threshold Peak Crest Soft Knee and 8 8 BI NV EEE 8 8 m T 8 SVR VANE mcn 9 SI DOCHA MES ECO DI 9 10 FSS RIS ee a 10 Transfer function gain reduction display 11 Brecise ECO MOSS a ane ad a a a NEU UR EDDIE M UH n FED ONERE M ESI 11 Br r 11 soc M 11 COntrols ANG Re elo E EET OE T Omm 12 Technical SbeclfiCallODS casu dava UP M ar ne nos Orco RR eos vaL S PD S care eee aride 12 insi c
6. Z Peak speed for recovery Long term events switch to Slow Release speed Dual release paths offer a wide range of musically useful options For example single drum peaks can be allowed to recover quickly to avoid dulling and breathing side effects At the same time sustained content like bass lines or synth pads can recover slower and thus strongly reduce typical side effects like pumping and distortion 10 We recommend a Release Peak value between 25 200ms and Release RMS values above 160ms for complex content such as mixes Faster settings are useful for particularly dynamic material like solo drums percussion and acapellas Because the peak path is much more sensitive than the RMS path setting the Release Peak to a higher value than Release RMS while keeping the Peak Crest low practically disables the RMS part of the compressor In other words the algorithm reverts to a single stage release and behaves much like a common peak compressor To disable the Peak path of the compressor set Peak Crest fully clockwise and set Release Peak fully counterclockwise TRANSFER FUNCTION GAIN REDUCTION DISPLAY The Transfer function graph shows the current in out gain transfer function of the compressor The solid line shows the compressor s overall transfer function the half transparent line above represents the transfer function of the peak path which is always Peak Crest dB above the RMS path s transfer function
7. ak Crest adjusts the threshold of the peak path relative to the main Threshold A Peak Crest of zero sets both paths to equal thresholds a high Peak Crest increases the threshold of the peak path in order to compress fast events transients only for higher levels and nearly disables the peak path Soft Knee adjusts the threshold transition softness Lower knee values create a sharp transition at the threshold point while higher knee values will compress more gradually but also deeper than the threshold Peak Ratio In default mode both peak and RMS paths use the same compression ratio In LIM mode the peak path always uses a fixed ratio of 7 1 while the RMS path ratio is still controlled by the ordinary Ratio control Ratio defines how strongly the signal will be compressed as it exceeds the threshold The range is fully continuous between 1 1 and 7 1 i Soft knee reduces the effective threshold i The threshold affects compression based on the compressor s output level not the input level The higher the compression the lower the detection signal will be The threshold effectively rides on the signal instead of accurately tracking its overloads MAKEUP GAIN MAKEUP Make up gain is used to compensate the gain reduction introduced by the compressor The makeup control can also attenuate the compressed signal up to 60dB which is useful for parallel compression techniques DRY MIX DRY MIX Dry Mix blends the o
8. e output of the compressor That is the compressor listens to what it has done This interesting topology is common in the analogue domain mostly due its better cost efficiency and the restrictions of certain circuits From a technical point of view the feedback structure has several disadvantages Typically it s much more difficult to control and distortion is significantly higher and compression dependent by design It has difficulty achieving ratios higher than approximately 3 1 and the maximum amount of gain reduction is limited On the other hand the feedback approach has some musically related advantages Most of all a very natural compression behavior and interesting harmonic distortion distribution The compression timing and ratio is program dependent and seems to naturally adapt to most sources quickly No complicated tweaking is required for the compressor to sound good in most situations This is the route we took with the project of building the TDR Feedback Compressor PRECISION ALIASING AND THE SOLUTION Controlling the dynamic range of an audio signal in the digital domain is not as easy as it looks A whole array of problems makes it very difficult to build a truly effective and musically attractive compressor in the digital domain The most significant restrictions are due to the discrete i e stepped nature of digital signal storage Without delving too deep into the mathematics we have to keep in
9. ents of the mouse make large changes and slow small movements allow for fine tuning of settings You can also double click a control to reset it to its default value TECHNICAL SPECIFICATIONS Available binaries 32bit and 64bit VST AU Input Output resolution 32bit floating point Internal resolution 64bit floating point Latency 184 samples at 48kHz or below 8 samples for higher sample rates Supported sample rates From 44 1kHz to 192kHz Supported channel configuration Stereo GET IN TOUCH Ideas Bugs Improvements We want to hear your feedback You can easily reach us via one of the websites below Check out the Tokyo Dawn Labs website for feedback news updates and downloads http www tokyodawn net tokyo dawn labs You can also directly head to the TDR Feedback Compressor page http www tokyodawn net tdr feedback compressor 2 Tokyo Dawn Labs is closely affiliated to Tokyo Dawn Records so make sure to check out their artists and releases http www tokyodawn net END USER LICENSE AGREEMENT End User License Agreement This software is provided free of charge but Tokyo Dawn Records retains copyright You are not allowed to redistribute this software without explicit permission from Tokyo Dawn Records You are not allowed to sell or to rent this software You are not allowed to reverse engineer this software You are allowed to use this software for educational and artistic application including commercial mus
10. ic production This software is provided as is without any express or implied warranty In no event will Tokyo Dawn Labs be held liable for any damages arising from the use of this software 12
11. linked STEREO DIFF Full right 100 means that the compressor fully preserves the original stereo image under all circumstances Technically the channel with the highest level controls both sides equally This is how most modern compressors are linked for stereo operation Full left 0 is equivalent to a sum based stereo link That is both sides are mixed and the sum of them controls both sides equally This is how several old compressors used to link the two mono channels for stereo operation While this mode also perfectly preserves the position of the stereo center the stereo width is allowed to change depending on compression and material Technically the compressor ignores the stereo difference information This control differs radically from the stereo link unlink option found on most stereo compressors The Feedback Compressor II is never allowed to shift the stereo center which could occur if unlinked operation was permitted ATTACK ATTACK The Attack time controls how long the compressor takes to reach full gain reduction Fast attack times respond quickly to level changes in the sidechain Slow attack times on the other hand respond more slowly and smoothly letting small events transients pass through the compressor without gain reduction Note that the Feedback Compressor II offers particularly fast reaction many times smaller than a single sample However attack times that are too fast can easily distort lo
12. mind that the data saved in audio files is not the actual analogue audio signal It is an intermediate format The true signal is only reconstructed after the anti alias filter in the DA converter But if one wants to control the amplitude of music accurately it is absolutely essential to know the actual waveform Another huge problem in digital dynamics control is a phenomenon called aliasing or Moir images Aliasing appears all in discrete i e stepped systems as soon the frequency of a signal exceeds the Nyquist rate half the sample rate The evil detail here is that contrary to analogue systems signals exceeding the bandwidth aren t gradually faded out instead they mirror at the Nyquist frequency and move back into the audible range at full energy and mirror again at DC and at Nyquist again and again Compressors are non linear systems All non linear systems add harmonic and non harmonic content to the processed signal and thus extend the bandwidth significantly The more aggressive the non linearity the stronger and higher the newly generated artifacts If the sample rate is too low to handle the extended bandwidth all these harmonics will alias and lose their harmonic relation to the fundamental resulting in an unpleasant sound The TDR Feedback Compressor Il s algorithm was carefully designed to avoid these issues To achieve this in efficient manner the algorithm is split in two parts both running at highe
13. r rates than the original signal Gain Cell The gain cell is a central part of the compressor and the place where audio signal s level is adjusted by the control signal delivered by the sidechain Such an operation is a non linear process and doubles the bandwidth To handle this bandwidth this multiplication always runs at least at twice the audio sample rate i e at least 88 2kHz One interesting design feature of TDR Feedback Compressor Il is that only the compressed portion of the signal listen via Delta switch is oversampled This leaves the original signal completely untouched as long as no gain reduction is occurring the plugin is 100 bit transparent Sidechain The sidechain is responsible for generating a control signal for the gain cell It consists of several complex non linear elements such as the threshold and timing filters To avoid aliasing in the control signal which would severely limit the accuracy of the compression the sidechain runs at a very high rate of more than 352 8kHz In both cases the resampling is done via very high quality linear phase time domain convolution Note that these quality improvements come at a price CPU cycles But from the sonic point of view they are well worth the costs CONTROL SCHEME The Feedback compressor Il is a relatively complex compressor which allows access to a wide range of advanced parameters To better understand all the controls and full range of options it is
14. riginal signal into the processed i e compressed part It enables the use of parallel compression techniques upward compression NY compression without complicated fy routings or DAW latency compensation issues 20 0 dB Dry Mix and Make up Gain form a 2 channel mixer Dry mix is not a 0 100 Dry Wet control OUTPUT GAIN OUT GAIN Out Gain controls the output of the compressor without affecting the balance between 0 0 dB compressed and dry mix signals SIDECHAIN HP FILTER The Side chain High Pass Filter section allows control over the compressor s sensitivity to low MP FILTER frequencies That is the compression threshold becomes frequency dependent and thus less SLOPE responsive to low frequency content Three different high pass filter slopes are supported 6dB Oct 3dB Octave 6dB Octave 12dB Octave The 3dB Oct filter deserves special attention It consists of a special filter network which approximates the inverse pink noise distribution This is probably the most reasonable sidechain pre processing because it basically helps the compressor to take into account the typical frequency distribution of music signals The 3dB Octave slope of pink noise This mode performs particularly well on complex material The filter s crossover point can be set between 30Hz to 400Hz SIDECHAIN STEREO DIFF EC Side Chain Stereo Difference controls the way compression of left and right channels is
15. w frequency content so be careful with its use RELEASE PEAK RMS RELEASEPEAK 8 RELEASE RMS The timing section differs slightly from the typical layout found on most compressors The TDR Feedback Compressor can dynamically select the most 4 O suitable release path depending on the program material Two virtual LEDs F indicate the currently active release path and controls Release Peak defines how quickly gain recovers after short overloads i e fast transients Release RMS defines how fast gain recovers after sustained gain reduction The following image shows a test signal before and after compression It consists of one short event such as a snare hit a long term event and some background noise in order to make the effect more visible As you can see the reduction triggered by the short transient recovers much faster than the reduction caused by the second over threshold event B 1900 20 000 30000 amp 40 000 50000 amp 60 000 amp 70000 amp amp 80000 amp 90000 amp 100 000 amp 110 000 amp 120 000 1130 000 140 000 159090 0000000 000050 00 000000 000001500 00 00 02 000 00 00 02 500 00 00 03 000 00 00 03 500 hate on ee ie a ne ndm a a aes diate m Fran m i io Short overloads use Release
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