KnowledgeBase | K2500X | Program Mode


Gain Staging Tips

Question:

How can I make best use of the K2's internal gain structure?

Answer:

Gain Staging Tips for the K2000/K2500/K2600/K2661:

There are several place in a typical V.A.S.T. program in which you can increase or lower the Gain. The following tips should help you understand how they work and what strategies you should apply for getting the best possible signal out of your Kurzweil. First we will discuss the basic voice gain structure, then we will discuss the "output" gain setting.

The gain path for one voice is primarily controlled by the algorithm for that voice's layer. The order (flowing from left to right) is pretty well made clear by the diagram, but a little explanation is needed. First of all, the samples in ROM or RAM have at least 6dB of headroom built in due to the way the V.A.S.T. synthesis chip processes samples. If a sample is not normalized, there will be more than 6dB of headroom. Typically in our programs this is all eaten up by the adjust setting on the F4-AMP page, which is often set to be +6dB or more. If we assume that we are using Algorithm 1 and the F4-AMP page is set to all zero, and we select the parametric EQ function with no pad, then we can always boost the EQ gain (F3-AMT) at least 6dB before that voice will exhibit clipping. Padding the input to the EQ on the F1-FRQ page will give even more... 18dB pad will give a total of 24dB headroom available for boosting the EQ. Of course different frequency ranges of different sounds have more or less energy, so with EQ you actually can often apply more dB's of boost than you have headroom (the frequency range you are boosting may be many dB below the overall level of the sample) but if you are boosting near the fundamental it will work a lot like simple gain in terms of headroom. Due to the ordering, if you boost the parametric EQ until it's clipping, no amount of turning it down at the F4-AMP page will correct it (as the clipping is occurring prior to the F4 block). Each box in the Alg that applies gain must be aware of/provide it's own headroom.

In comparison to samples, V.A.S.T. generated waveforms do not have any headroom built in, they are full scale, except that the "saw+" and others that mix with the sample have 6dB headroom built in (so it won't clip when it adds 'em, but once they're added, not much headroom is left). The output of the distortion, wrap, shape, etc. tends to be full scale or near it when the distortion is audible. Padding down the input to these doesn't help, it just subtracts from your adjust setting. The mixers (+amp) pad both inputs down 6dB before mixing to prevent clipping, but the output of the mixer will then tend to be near full scale.

All of this implies that you usually cannot set F4-AMP higher than 0dB unless the signal is filtered, cut, or padded somewhere along the line, or unless you apply no DSP, in which case you can always boost at least 6dB there. Don't forget that KeyTrk can cause clipping, as can Control Source 1 and 2. Velocity tracking on the F4-AMP page will never add clipping though, it actually subtracts gain. Velocity tracking on other functions often does add gain. Most layers created by soundware have been tweaked so that there is little or no headroom left, as soon as the user goes to add more boost anywhere, it will clip. Low pass filters, high pass filters, bandpass filters, and EQ cuts, all reduce gain, providing any box following them (to the right) with more headroom.

About Output Gain:

For the K2000, v3.18 or earlier or the K2500 v2 or earlier, the OutGain setting on the MIDI Channels page simply replaces the one on each layer of that channel's program (the Gain parameter on the OUTPUT page of the program editor).

For the K2000 v3.54 or the K2500 v3 or later, or any K26 model, the OutGain parameter on the MIDI Channels page adds or subtracts the selected dB amount from the amount specified on the layer settings in the program. A setting of "Prog" makes it use the output gain programmed for each layer. The output gain specifies how much gain to add when summing a voice onto the DAC with the other voices.

If we assume that each voice's individual gain structure has been tweaked to be just below clipping, then an output gain setting of 6dB will tend to prevent "group" clipping when max voices are playing. If you were only playing a single voice, you could set the output gain as high as 30dB without clipping, but then when you played a second voice, both would clip. One method used to maximize programming flexibility is to set the first pad in the Algorithm to 18dB, set the F4-AMP adjust to 0dB, and set the output gain to 30dB. Initially this is similar to (prog 199) no pad, F4-AMP set to 6dB and output gain set to 6dB, but with things turned down at the beginning and middle of the signal path, and turned up at the very end (output). The overall gain has not changed. Now a parametric EQ could be boosted with no clipping, just turn down F4-AMP to compensate for the increased overall volume. If you were making a kick drum, for ex., and wanted it to be a bit louder than other layers, just turn up F4-AMP, instead of having to go to the output page.

The disadvantages to this method are:

  • increased likelihood of audible quantization noise from the EQ due to shifting the input down 18dB
  • increased likelihood of getting "group" clipping (although little or no chance of individual channel clipping)
  • it doesn't work well for many algs/functions, esp. those that use distortion type functions or V.A.S.T. waveforms.

Finally, one last note, be aware that MIDI volume effects the F4-AMP page, by turning it down. You may have noticed that some patches sound different and/or better when you adjust MIDI volume, this occurs when the patch clips the F4-AMP page.


Need more info? Check out the following links: