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Q&A February 2002

Your Technical Questions Answered
Published February 2002
By Various

Q. What causes soft‑synth latency?

I'm interested in buying a built‑for‑audio PC, so I tried out a Carillon, specifically to find out how soft synths would sound. I have not used soft synths before, but I didn't expect so much latency. The advisor in the shop told me it was to do with the soundcard, but I would have thought it would have more to do with the processor. Can you give me an idea of the main factors affecting soft synths in terms of latency and sound quality?

Andrew Sharpe

PC Specialist Martin Walker replies: Latency is, indeed, a result of the soundcard, although the speed of your processor is also involved as well as the design of the soft‑synth in question. To ensure the smooth flow of audio from any audio application, whether it's a sequencer such as Cubase VST, Logic Audio or Sonar, or one of the many software synthesizers that can run either inside these applications or in stand‑alone mode, the soundcard drivers employ a small number of RAM buffers.

Latency can be an issue when it comes to soft synths: a modern soundcard design and fast computer processor are key requirements for avoiding problems.Latency can be an issue when it comes to soft synths: a modern soundcard design and fast computer processor are key requirements for avoiding problems.These are regularly filled up by the soft synth with audio data, which can then be clocked out smoothly by a small low‑level routine that has a high enough priority to ensure that, whatever other PC activities need to be carried out, the audio still has enough time to emerge without interruption. Meanwhile, assuming your PC processor is powerful enough, the soft synth will also get plenty of time to periodically perform the calculations that determine what waveform data goes into the buffers.

The time between pressing a key and hearing the sound from the software synth (the latency) is determined by the size of the soundcard buffers and the sample rate, so that (for instance) with a 512‑byte buffer and the most common 44.1kHz sample rate, it would take the synth sounds 512/44100 seconds, or 11.6 milliseconds, to emerge. This time delay is virtually unnoticeable by most musicians, who won't normally find soft‑synth latency annoying until it exceeds about 20 milliseconds.

Soundcard buffer size can nearly always be altered, and the lowest practical value (and therefore shortest latency) is determined by how well the drivers have been written, how fast your PC processor is, and how well Windows has been set up to suit the special requirements of audio recording and playback. The smaller the buffer size, the shorter the interruption that it can cope with before you get a glitch in audio playback.

Given that even the cheapest Carillon PC contains a powerful 866MHz Pentium III processor, and has been expertly set up for use by musicians, any noticeable soft‑synth latency must be due to a conservative soundcard buffer size. I've reviewed the majority of the soundcards used by Carillon in their systems, and there's no reason that their latency should need to be any more than 11.6ms to avoid glitching, which makes it virtually unnoticeable. Therefore I can only think that the particular model you tried hadn't been set up properly, or that someone had mistakenly altered some settings. Many musicians are finding that they can use even smaller buffers, and regularly achieve soft‑synth latencies of 6ms or even lower!

As for sound quality, although this is ultimately determined by the D‑A converters and output circuitry of the soundcard, it's far more dependent on the soft‑synth algorithms. These determine such factors as basic waveform purity, filter characteristics, smoothness of envelopes, and so on. Some may also provide internal options to improve sound quality at the expense of higher processor overhead, so you should always judge soft‑synth performance on a combination of sound quality and how much CPU power is used.

Q. What's the best thing to do when my old gear begins to wear out?

I have a Boss DR660, which I have had for about four years, on which the velocity pads appear to be wearing out. They have become so sensitive that anything above the most feather‑light tickle produces a MIDI velocity of 127. I also have a Roland PC180 which, on certain keys, is exhibiting the same behaviour. What exactly happens when these things wear out out, and is the same fate waiting for my Nord Lead? Is this an expensive repair job?

Owen Turley

Assistant Editor Tom Flint replies: Everything will wear out eventually, and I'm sure the Nord Lead is no exception. Pressure pads and mechanical moving parts like keys are prime candidates for going wrong, and you may also find that buttons which are used a lot will give out eventually too.

If you decide to get the keyboard and drum machine repaired professionally, it's either a case of sending them back to Roland for their service department to fix, or finding a specialist repair centre (there are a number of good ones listed in SOS's classified ads). If you take them to a Roland dealer or shop they will probably just send your gear back to Roland or to a specialist repair centre anyway, and will charge you accordingly. Bear in mind that any company repairing your synth will charge for parts, labour and VAT, which could add up to the second‑hand value of your equipment. Boss DR660s can now be bought for about £120 (see the SOS Readers' Ads at www.soundonsound.com/adverts). I'm sure you can get a second‑hand PC180 very cheaply too, but Edirol currently sell a PC180A MIDI Keyboard Controller for around £89 including VAT, and that is bundled with a copy of Steinberg's Cubasis AV MIDI + Audio sequencer. At that price it might just be worth buying one new; buying second‑hand gear can take a lot of time and effort and there is always the chance that the item you buy is wearing out too.

If it turns out that the repairs on your gear will be more expensive than buying second‑hand (or new) replacements, you might want to try fixing the equipment yourself. I'm sure your old gear won't have a warranty to invalidate, so it's certainly worth opening it up and taking a look inside. One possibility is that dust and general grime could be gumming up your keys and pads — something as simple as that could affect MIDI triggering. It's also possible that some moving parts are out of alignment or that a wire or two has worked loose and your problems may be fixable by pushing something back into its correct position. While you have your gear open, check the keys and pads to make sure they are not wearing underneath in any way. It is likely that you will be able to replace parts like these yourself, and a call to Roland (Roland Spares +44 (0)1792 515020) will soon enable you to find out if the bit you want is available. Roland UK's service department stocks a wide range of spare parts. If the keys and pads show no obvious signs of wear, the trouble might be wearing circuit contacts which the pads and keys press on.

Finally, under no circumstances allow your keyboard or drum machine to be powered up, or even just plugged in to the mains while you are poking about inside it — even if you are are sufficiently careful not to electrocute yourself, it is surprisingly easy to damage microprocessor‑based circuitry simply by shorting out of a couple of contacts.

Q. What extra gear should I buy to make dance music?

Q&AI am a frustrated musician in dire need of information. I want to write dance/trance music and don't really know how to go about it. I have a Korg X3 workstation (which I am still exploring), and a PC with Cubase VST. I'm planning to also get Reason. It has been suggested that I buy a Korg Electribe. Is this the right way to go? When I buy extra gear, how do I connect it all — ie. how do I use MIDI thru? And do I need to get a mixer when it comes to recording?

I also have found that I can only have two effects over the whole sequencer in my X3. Is there some way I can apply effects to separate channels?

Michael Grant

Assistant Editor Sam Inglis replies: There are several Electribes, in fact — a drum machine, a synth, a sampler, and a fourth one which combines bits of the others. For most types of dance music, these will all add a lot to the range of sounds you get in the X3. Probably the most important thing for dance music is a good source of drum and percussion sounds: you could try the drum machine, but I recommend you consider getting a sampler. The Electribe is a good choice, but you could also check out Yamaha's SU200 and the Boss SP202, or more sophisticated instruments like Akai's MPC2000XL. A sampler is the most flexible instrument for drum programming, and you can use it for other instrumental sounds too.

Regarding how to connect everything up via MIDI, it's best to have a separate MIDI port for each instrument, especially if you'll be using more than one instrument to generate MIDI signals as well as to play them back. In other words, if you're happy to play all your sounds from the X3 and use whatever other instrument you get simply as a sound source, you could just connect the MIDI Thru on the X3 to the MIDI In on that instrument (you'll need to set up the X3 and the other instrument to respond on different MIDI channels, though — remember that each MIDI port carries 16 MIDI channels). If, however, your other instrument is a drum machine (for example) and you want to play drum parts on the pads and have your computer sequencer record them, you'll need to be able to connect a MIDI Out from the drum machine to a MIDI In on your computer. (I'm assuming you're using Cubase to do the MIDI sequencing, rather than the sequencer built into the X3.) You could buy a MIDI merge box to merge the MIDI Outs from the X3 and drum machine, but it would be a lot better to get a MIDI interface for the PC that has more than one input and output.

As for whether you need a mixer, it's up to you. If you have lots of hardware instruments and you want to hear their outputs all at the same time, you need one. If you have only one or two, you could just get a multi‑input soundcard and mix and monitor via the PC.

The X3 has only two effects generators, so you will only be able to use two effects programs at a time. You should, however, be able to apply different amounts of each of these to the different parts in your tracks.

Finally, if you plan to buy Reason (which is a self‑contained music‑making system, including sounds and samples), it might be just as well to wait until you have checked out the sounds it generates. If you're happy with them, you might find you don't need to buy extra hardware instruments at all.

Q. How can I stop my music annoying my neighbour?

I've converted my loft so that I can practice my sax. Walls, floor and ceiling are padded with rockwool, and the floor has thick underlay, plus carpet. The doors are solid fire doors, but still the sound is travelling through the house (a three‑bedroom semi). The walls and ceiling are plasterboard, skimmed and painted. Is there anything else I can do to prevent annoying my very unhelpful neighbour?

Mick Cape

Editor Paul White replies: Putting Rockwool on the walls may improve the acoustics but does little to help with soundproofing. The fact that you have plasterboard walls and ceilings is probably the biggest problem, but the only way to improve these is to add mass. If the structure is strong enough, I suggest adding a layer of lightweight fibreboard and then the thickest plasterboard you can buy, on top of that. You'd need to get the whole thing reskimmed, but it should cut down significantly on sound leakage through the walls. You might even want to add an extra layer of plasterboard to the wall facing the neighbour.

If you're getting too much transmission through the floor, consider making a simple floating floor by putting chipboard flooring on top of a layer of rockwool. Use two layers of chipboard screwed together, to get enough strength and rigidity. Be aware that your fire doors may still leak sound around the edges, so check that the seal touches the door all the way along all four sides when the door is closed. These measures will undoubtedly improve the situation, but sound travels through houses in mysterious ways, so the practical results aren't always quite as calculated!

Q. Can I ensure that my CDs will play on all hi‑fi systems?

Q&AI have a couple of completely unrelated queries for you. First, I am aware that certain CDRs will not play on certain hi‑fi systems. Obviously, commercially released CDs don't suffer from the same problem. Is this because the burning process for commercial releases is different, or because the discs themselves are different? If I send a master to a duplicator (such as the ones who advertise in your magazine), how can I be sure that the resulting CDs will play on any hi‑fi? Or is it possible to overcome the problem with my own duplication?

Second, I'm interested in getting into guitar synthesis, but it seems limited to dedicated units such as the Roland GR33. What I really want to be able to do is control any synth module or keyboard with my guitar. Can you suggest any devices that would help me do this? (By the way, I want to do it live, so software wouldn't be suitable.)

Jonathan Boyle

Assistant Editor Sam Inglis replies: Different brands of CD‑R, burned at different speeds, may make a difference, but the underlying reason is that pressed CDs are more reflective than CD‑Rs, and some player mechanisms are insufficiantly sensitive to read them. Duplicators should be able to advise you on the best choice of CD‑R media, but if you want to guarantee that your CDs will work in all players, having them glass‑mastered and pressed is the only sure solution. If you want to get 500 or 1000 copies pressed, this is often the most cost‑effective way of doing it in any case.

To control MIDI syths with your guitar, you'll need to add a MIDI pickup and an interface. These convert your playing into MIDI note data, which can then be sent to the synth or sampler of your choice (provided it's MIDI‑compatible, obviously). Although Roland's GR33 has a built‑in synth, it does in fact give very good results with external units via MIDI. Other MIDI pickups to look out for are Yamaha's G1D/G50 system (reviewed SOS December 1996) and Blue Chip's Axiom AX100 (reviewed May 1998).

Published February 2002