This Chapter explains how to make use of sampled sound to enhance your programs. For users restricted to the Amiga's internal floppy drive, AMOS Professional allows a range of superb "live" sound effects and musical tones to be called up. If you have access to a hard drive or CD- ROM, the AMOS Professional Double Buffered Sampling system offers full exploitation of sampled sound. There is even a built-in "recording studio" ready to be used, and you can enjoy the facilities of this Sample Bank Maker accessory, which is featured in Chapter 13.6 of this User Guide.
Modern computers are able to store sound frequencies in the form of digits. Your Amiga is a digital sound synthesizer, and AMOS Professional is ready, willing and able to harness its power. There are many digital sound samplers on the market, ready to be plugged into your computer for grabbing sound samples off CD, cassette, radio and microphone. Unfortunately there are two restrictions in enjoying these sources for digital sound. Firstly, sampler cartridges are rather expensive, and secondly, stealing other people's audio creations is illegal! Luckily, there are thousands of public domain sound effects and musical instrument samples that AMOS Professional can import and transform for your own purposes, perfectly and legally. AMOS Professional sound samples are held in their own memory banks, and bank number 5 is usually held as the default sample bank.
Playing a sound sample
SAM PLAY
instruction: play a sound sample from the sample bank
Sam Play sample number
Sam Play voice,sample number
Sam Play voice,sample number, frequency
The SAM PLAY command is used to play a digital sound sample through your audio system. Simply define the number of the required sample held in the bank. There is no limit to the number of samples that can be stored, other than available memory.
There are two optional parameters that can also be given. A voice parameter can be placed immediately after the SAM PLAY command, in front of the sample number. This is a bitmap containing a list of the voices the sample will use. There is one bit for each of the four available voices, and to play a voice the relevant bit should be set to 1, as explained in the last Chapter. The other parameter can be given after the sample number, and this governs the frequency of the sound. The frequency parameter sets the speed at which the sample will be played back, and the setting is given in Hertz. This is a professional standard of measurement, but as a rule of thumb, a rate of 4000 is acceptable for simple sound effects, with 10000 for recognisable speech. By changing this playback rate, the sample pitch can be adjusted over a very wide range, allowing a single sample to generate many different sounds.