Analoguesque - Soundfont Tutorial

Sound Designs

Setting Global Loop Points

In the previous chapter we succeeded in importing our 4 base samples. To complete the creation of these samples as oscillators, we need to loop them successfully, and the way we do this is by using Vienna's Global Loop Editor.

Double-Click on the sawtooth-A4 sample. This brings up the sample into the Global Loop Editor. Click on Loop Settings >> to bring up the actual editing window, as shown in Figure 4.1.

Figure 4.1

Since this is a Global Loop (I.e. applied to the entire SoundFont^® Bank whenever this sample is used in an instrument), the Local Sample Start and Local Sample End are disabled. Our main concern is the Global Loop Start and Global Loop End, which is what we use to set our actual loop point. The graphical area below these 2 points shows the end and start loop points: End = Blue; Start = Green. It makes sense to show the end point first because this is essentially how a loop works: The sample plays to the end, and then loops back to the start point again, so you would want to see this transition from end to start.

As you can see from the default settings in the top waveform window, Vienna mysteriously has the Start and End points set a few samples from the start and end of the sample. In fact, you cannot start the loop at 0, or end it on the last sample. There seems to be a 6-sample buffer zone on either end of a sample. If you remember back to generating the waveforms in Cool edit, you will recall the suggestion of saving each sample with a little more than 1 cycle of the waveform. This 6-sample buffer is one of the reasons why.

Looking at the lower waveform window, you can see that there is no smooth transition between the end and start loop points of our sample. The waveform is moving upwards, and on reaching the end point, suddenly continues from a point closer to the zero cross point - an audible glitch. Sonically this will result in a clicking sound each time the sample loops, destroying the notion of a pure waveform. This is a Sawtooth waveform, and to make it sound that way we have to loop it perfectly without this click. Use your mouse to alter the start and end loop point by clicking on the spinner buttons, just to get a feel of how it works. You will see how the waveform moves in tune with the spinner buttons. You can also drag the start and end loop point indicators in the top waveform window, by clicking and dragging them. This will also alter your spinner results in a more macro manner.

To look at this more closely, move your mouse into the transition window (you will notice a + magnifying glass appear) and left-click in the window. This zooms in on the loop points so you can get a closer look. Right-clicking in the window zooms out. Figure 4.2 shows a fully zoomed view.

Figure 4.2

Now you have a better view of how the loop-end matches the loop start, and as you can see, it doesn't match at all. What we need to do is click the Global Loop Start spinner button and increase the value. As the value increases, the start loop point approaches the end loop point (Figure 4.3). The setting in Figure 4.3 will still cause a click, but it becomes less pronounced as the Green Loop Start approaches the Blue Loop End.

Figure 4.3

Sometimes what you see graphically is not a 100% true sonic reflection of the loop-point. For instance, we may have moved our start point until it seemed perfectly looped as in Figure 4.4.

Figure 4.4

Looking at it, it seems perfect, but there is a way to pick up the slightest loop errors:
In the loop editing screen there is a setting for the playback pitch of the sound, called Key Number. It defaults to C4, so your sample plays back at midi key C4. Very often if you play at a lower key, you can hear loop imperfections much more clearly, so set this to something lower than C4, say, C3, or C2 ... etc. Try playing back the loop now, and you might hear a faint click. The problem may not be very obvious with a Sawtooth waveform, but with a Sinewave it is painfully noticeable! At this point you can simply fine tune your loop start until the glitch disappears. It does so at Loop Start = 30 samples, as in Figure 4.5. Obviously when you don't hear a click in the loop then it's probably perfect!

Figure 4.5

When you hear your sample looping clearly and without clicks and pops, you're done. You now have a Global Loop setting for your sample. Each time you import the sample into an instrument in the Instrument Pool, this Global Loop Point will be taken as the default. From this point on your sample will always be perfectly looped, no matter where you use it.

A point to note is that looping samples can be an extremely difficult process. It takes a lot of practice, patience, and dedication. Some people have a natural skill, and others don't, but in the end you can triumph with enough practice. In some cases you will encounter samples that simply cannot be looped cleanly. This is generally not the case with simple single-cycle waveforms like we are using, but it becomes apparent with more complex samples.