When sampling technology finally became accessible to mere mortals and not just uber-rich Fairlight and Synclavier enthusiasts, the race was on to increase fidelity and leave behind the limitations of those first 8-bit samplers. Bit depth and sampling rates increased and memory capacity expanded until the average sampled sound was indistinguishable from the same sound recorded on a CD. But sure enough, after many years of enjoying the pristine sound quality of the new sampling technology, musicians began to explore and exploit the limitations of the old school samplers. Suddenly the grain of low bit-rate samples and the metallic grit of aliasing is very much in style. So how can you emulate the sonic artifacts of some of the long forgotten vintage samplers? I'm glad you asked...
1.) Buy a Vintage Sampler
Of course the simplest and most direct way to get that vintage sound is to buy an actual vintage sampler. Hardware sampling technology, unlike analog synths, has only gone down in value after the arrival of software samplers, so for the most part, you can get most vintage samplers for relative pocket change. The downside of this is you have to deal with learning each sampler's OS - and rest assured, try programming an Ensoniq Mirage with its 2-digit hexidecimal LED display and you will never complain about a soft synth's GUI ever again, no matter how hideous. You also have to deal with finding outdated storage formats to save sounds to. So while this is the best way to get that vintage sound, it is not without its hassles. That said, I keep an old Ensoniq EPS-16+ around soley for this purpose and wouldn't dream of selling it.
2.) Playing with Bit-Depth
You have a Bit Crusher among your arsenal of plug-ins, right? (If you say you don't, you're wrong, look again. Or go download this free one from Togu Audio Line). One of the two main controls you'll find on any self-respecting bit crusher is for Bit Depth. Bit depth refers to the number of bits used to store each sample of a piece of audio. If you're trying to replicate the sound of a specific bit of gear, it helps to know what bit depth the original device offered. Akai's popular S-series samplers and Emu's Emulator III were 16-bit samplers. Ensoniq's original EPS was actually a 13(!)-bit sampler. The infamous MPC-60 drum machine from Akai was 12-bit. The original Emulator, the original Fairlight, and the Ensoniq Mirage were all 8-bit. Those obnoxious little sound chips you occasionally find in greeting cards are usually 4-bit. Since bit-depth largely governs the dynamic range of a sampled sound, you can also try compressing your sounds a bit more aggressively the lower the bit-depth you are trying to emulate is. But if you take nothing else from this blurb let it be this: 12-bit is pure magic on drums. For realsies. Just try it.
3.) Abuse Your Sample Rate
As you may have guessed, the Sample Rate is the other major component you'll find on just about any bit crusher type effect. The sample rate refers to the number of tiny 'snapshots' of a sound your sampler is taking per second. More samples per second results in a more accurate representation of the original sound in the same way a picture taken on your cell phone is never going to look as nice as your friend's super expensive SLR camera. Conversely, however, the lower you take the sample rate, the harder it is for your sampler to construct an accurate picture of your sound. Lower the sample rate enough and you will hear an artifact known as Aliasing. Aliasing is a sort of metallic, "robotic"sounding distortion that results when the sample rate isn't adequate enough to accurately reproduce higher frequencies and the sampler attempts to recreate it with what it has available and fails miserably. It's an error, essentially, and one that can be exploited for some really great effects. While aliasing was something most people wanted to avoid back in the early days of sampling, the miniscule memory limitations on these early machines meant lower sample rates were often used to save space, so it was often an inevitability. Indeed, most samplers had a limitation built in as to what the fastest sample rate could be. The key here is subtlety. Going overboard can sound great, but it doesn't reflect the way we used samplers back then. In general, make longer samples have a lower sample rate, as it was these larger samples that required sizing down the most. Add just a little bit of the digital grunge and you'll be a long way towards replicating the sound.
4. Keep it Short
As I just mentioned, RAM was very expensive in the days of the early samplers, so most of these machines had almost insanely small memories. 512k and 1 or 2 MB limitations were not uncommon. And that's not a per instrument limitation, that is your TOTAL memory. One thing these memory limitations lead to was abnormally short sounds - often a bit abruptly cut off. Sample developers were trying to squeeze out every spare fraction of a second they could. This is why crash cymbal sounds on so many early sampling drum machines and samplers sound very abrupt and unnaturally short. Looping was also commonly used to preserve space. Nowadays, we might just sample the entire length of a piano note, but back in the day, sample creators would attempt to find a place not far after the attack transient where they could simply loop a short fragment of audio, thus allowing them to use their samplers envelopes to shape the sound and store it in a fraction of the space. This obviously lead to more static, less natural sounding sustains on a lot of instruments, but it is an important thing to consider if you're after that old school sound.
5. What's Your Output?
One of the big differences between hardware and software samplers is in the output stage. With a software sampler, some cleverly written code recreates the sounds through the outputs of your sound card or renders the sounds direct to disc. On a hardware sampler, the sampler has its own outputs, which you then record into your sound card in order to play it back through the outputs of your sound card. That extra stage of output is a subtle thing, but it can definitely color your sounds. When I sold my Emu E6400 after I transferred my library over to Kontakt format, I immediately noticed a difference in the way the samples sounded. Drum sounds in particular lost a quite a bit of the low end warmth. Obviously different samplers had different quality converters and outputs, so surely some will color the sound more than others, but this is something worth considering playing around with a bit. Even if you aren't trying to perfectly replicate the sound of an old sampler, try using things like tape emulators or coloration plug-ins like PSP's VintageWarmer 2 to add a little bit of character to your sounds. You'll be amazed at what a difference a tasteful amount of audio coloration can make.