Midi Sample Dump Standard
Technology, Mind over Midi
Published by Keyboard/July 1989
Lachlan Westfall is the president of the lnternational MIDI Association
and a member of the Executive Board of the MIDI Manufacturers Association.
posted 3 october 2001
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One reason that Midi works so
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ONE REASON THAT MIDI WORKS SO well with so many different instruments is that the MIDI spedfication is not written in stone. There are no granite tablets sequestered in some high altar. MIDI is a cooperative venture, the product of a democratic process, and as such, the specification is a "living document." There have been many additions and refinements to the original MIDI 1.0 Specification (presently Document Version 4.1), each designed to meet the growing and changing needs of the electronic music industry.
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MIDI Sample Dump Standard (SDS), developed in 1985, was one of the first major additions to the MlDl Specification. Priort o SDS, musicians who wished to transfer sound data from one sampler to another had no alternative but to resample their sounds into the other instrumenL Fortunately, the format of sample data is relatively consistent from instrument to instrument, and since it is digital, the data can be transferred over MIDI.
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The first sampler to support SDS was Sequential's Prophet 2000. The instrument featured the unique ability to increase the MIDI baud rate (speed of transmission) during the sample dump process-cutting in half the time it took to dump the digital data. Unfortunately, this spawned countless "faster MIDI" and "MIDI 2.0" rumors, so the feature was never adopted by other manufacturers. Although the convenience of SDS elated owners of Prophet 2000s, the real fun started when other sampler and computer software manufacturers began to implement the standard.
Nearly four years after the development of SDS, the list of devices that support the standard has grown considerably (see side-bar), but not as extensively as many people in the industry had expected or hoped for. Today, only about half of the samplers on the market have SDS implemented. On the other hand,a number of graphic editing software packages support SDS. Programs such as Alchemy and Sound Designer allow samples to be edited and stored in a generic format, then use SDS to transmit the sound files to any sampler in your system-provided that your instrument is one of those supported by the program.
Although the Sample Dump Standard has made life easier for musicians with multiple samplers, it is far from perfect. SDS users often find that the words "generic" and "standard" don't live upto their dictionary definitions. If you are planning on using SDS, you may find it easier if you have a computer. Graphic editing software is usually designed to deal with the various idiosyncrasies of each sampler which means you won't have to. However, if you're determined to do a sampler-to-sampler transfer, here are some pitfalls to watch out for.
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The first thing to determine is whether your sampler can initiate a sample dump or send a dump request. In order to transfer a sample over MIDI, at least one of the devices must be able to initiate the dump, and not all samplers have this ability. For example, an Akai S900 is happy to send a sample when it receives a request from an external device, but neither dump requests nor transmissions can be initiated from its front panel.
Once you've found a way to initiate the dump, it's time to consider memory allocation. It's safe to assume that you can replace a sample in your instrument's internal memory with one that is the same size or smaller, but what if you try to replace a file with one that uses a higher sampling rate? Some samplers will allocate more memory as needed, but others may require you to manually "recover" memory or even create a "dummy" sample in order to accommodate the sample you wish to transmit. In addition to the size of the sample, check to see if your sampler can receive a sample in a memory location other than the one currently selected or if it can create a new memory location after the dump is received. If you have successfully completed a transfer and the simple doesn't appear where you thought it would, it is possible that the new sample is in an adjacent memory location. This is because each Sample has an identifying number and some manufacturers start their numbering with zero, while others start with one. Speaking of ID numbers: Although system-exclusive messages don't typically include MIDI channel designations, the Sample Dump Standard (and some other universal sys-ex messages) contains a MIDI channel or device ID - byte. If you are using multiple samplers, be sure to match these up correctly.
Another problem you may encounter involves the format of the sample being transmitted. The specification allows for samples containing as few as 8 or as many as 28
significant bits, but the original SDS format only used 12 bits. Today, however there are a number of 16-bit samplers, and thus 16-bit sample dumps. Theoretically 12-bit samplers, should be able handle 16-bit sampledumps, but most of the 12-bit machines were designed before the 16-bit machines arrived on the scene. As a result, they may not have been extensively tested for compatibility with 16-bit data. Some devices allow yo select the data format-12-or 16-bit. If you are sending 16-bit data to a 12-bit machine, choose the 12-bit format.This wil ensure compatibility and will speed up the dump, as a 12-bit word can be sent in two MIDI bytes, whereas a 16-bit word requires three.
SDS has two forms of transmission: open-loop and closed-loop. Open-loop (which requires only one MIDI cable) means that the sample is sent out "one way," In the same manner as standard MIDI information. Since the transmitter has no way of confirming that the receiver has had time to process the data, it must insert pauses in between the data bytes. Often these pauses are much longer than Is really necessary. In the closed-loop format (which requires that the MIDI inputs and outputs of both devices be connected to each other), the receiver can signal when information has been received and processed. This greatly speeds up the transmission of the sample and has become the preferred mode of operation for roost samplers and software packages. If you are dealing with multiple samplers, it is highly recommended that you invest in a MIDI switching box so you can quickly set up a closed-loop system with each of your samplers when transferring samples.
