Интервью с создателями Ямахи 2600, взято с сайта Ямахи
Engineers who developed the RX-V2600 speak. A discussion with creators from Yamaha
Hirochika Maegaki
Manager/Engineer
Software Development Division
AV & IT Business Group
Susumu Kumazawa
Supervisor/Engineer
Software Development Division
AV & IT Business Group
Yuki Yoshizawa
Supervisor/Engineer
Software Development Division
AV & IT Business Group
Hideyuki Suzuki
Supervisor/Engineer
Hardware Development Division
AV & IT Business Group
This article is based on interviews conducted on November 8, 2005 in the Home Theatre Room at Yamaha Corporation.
The core models in Yamaha’s Digital Home Theatre Receiver line-up, the RX-V2500 and RX-V1500, recently underwent a complete overhaul and upgrade. The result is the new RX-V2600 and RX-V1600. These new models are sure to attract attention due to features such as compatibility with HDMI version 1.1, digital video conversion functionality, and excellent specs that exceed those of other amps in their price range. The RX-V2600 and RX-V1600 have many additional points of interest however, including improvements in sound quality compared with earlier models and areas where they differ from the high-end RX-V4600, which was released somewhat earlier. In these interviews we ask the engineers who developed the RX-V2600 and RX-V1600, many of the questions users will want answers to, with a particular focus on the RX-V2600. The participants are Hirochika Maegaki, who had overall responsibility for development work on the RX-V2600 and RX-V1600, Susumu Kumazawa, who was in charge of the audio related aspects, Hideyuki Suzuki, who supervised work on the digital video circuitry and other video related hardware, and Yuki Yoshizawa, who handled software development, especially that related to HDMI.
1. Improvements to the power supply changed the sound.
Sound Quality
Delivering the sound and functions customers demand
— The long-awaited RX-V2600 has finally arrived. With the appearance of the RX-V4600, I was wondering if the RX-V2600 would be something similar. You really surprised me, though, with the unexpectedly high specifications and features like digital video up-conversion. Am I correct in assuming that your focus for this model upgrade was on improving performance?
Maegaki: We started our development work on the RX-V2600 by asking ourselves the question, “Just what do today’s customers want in an A/V Receiver?” This led us to set three initial targets. The first, it goes without saying, was to implement improvements that would make the sound quality even better. The second was digital video up-conversion, which you just mentioned. The third was to enhance usability through features such as HDMI and a new GUI.
— The fluorescent display now has two rows of text and clearly looks much easier to use.
Maegaki: Yes, that’s right. The second and third targets I mentioned are in fact linked. For example, if the amp has an HDMI terminal but there are limitations on the types of signals that can be output through it, ease of use—the biggest feature of HDMI—will not be realized. This is why we decided to include the capability of up-scaling analogue signals so they can be output via the HDMI terminal. The RX-V2600 has digital video conversion functions that simply cannot be found in other receivers in its class.
— That’s right. Until now even if the amp had HDMI terminals you had to connect separate audio and video cables to watch conventional analogue video signals. This new capability you have introduced is a really important step in realizing the full convenience of HDMI. Then there is the question of sound quality, of course. The RX-V2500 had a good reputation in this regard, but it seems you’ve made further improvements in the RX-V2600.
Maegaki: Yes, we have. Better sound quality is an area in which we’ve been working hard for quite some time, but with the RX-V2600 we felt we had to achieve a substantial improvement over the RX-V2500. We made a number of carefully considered enhancements, including developing low-noise power supply circuitry and employing discrete Burr-Brown DACs (digital-to-analogue converters) for each channel. I’m sure that Mr. Kumazawa will have a lot to tell you about in this area.
Reducing power supply noise still further
— Mr. Kumazawa, like Mr. Maegaki you worked on both the RX-V2500 and the RX-V2600. It would seem that even during development work on earlier models you were already paying a great deal of attention to improving sound quality.
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Kumazawa: Yes, that’s right. In particular, we positioned both the RX-V2400 and the RX-V2500, the two models preceding the RX-V2600, primarily in the nature of a Hi-Fi amplifier. We were therefore determined that the new RX-V2600 would live up to its predecessors in this respect and even better them. To ensure this we went still further along the same path to superior sound quality and added new developments.
— Specially, what is new in the RX-V2600?
Kumazawa: The biggest advances in the RX-V2600 are with the power supply, and the next most important improvements are in the DAC section. In the first area, we developed a new heavy-duty power transformer with independent windings for the digital video circuit block. This was done to prevent the digitisation of the video circuitry from adversely affecting the sound quality. In terms of capacity, the RX-V2600’s transformer is actually a size larger that that of the RX-V4600. It is about 1 kilogram heavier. Also, as in the RX-V4600, we selected Schottky barrier diodes for the rectifier diodes in the power block.
—The DSP-Z9 also employs Schottky barrier diodes, but isn’t this rather unusual in a Digital Home Theatre Receiver?
Kumazawa: They seem to be used in high-end pure Hi-Fi amplifiers, and I doubt if any other Hi-Fi amplifiers in this price bracket employ them due to the cost. Schottky barrier diodes cost about twice as much as conventional diodes.
— I know that Schottky barrier diodes are supposed to have low noise and contribute to good sound quality, but what exactly is so special about them? Can you explain the advantages to me in layman’s terms?
Kumazawa: Simply put, semiconductor devices such as diodes have a current flowing though them, which consists of moving electrons. Depending on the type of device, the manner in which the electrons start moving is different. The rise characteristics of a Schottky barrier diode are smoother than those of a conventional diode with a PN junction. This results in less noise when they operate. Also, Schottky barrier diodes supply current more efficiently, which also contributes to better sound quality.
— I see, so that is the difference. Schottky barrier diodes are also small, aren’t they? They appear to be about the same size as ordinary bridge diodes. Though I must say I am struck by the size of the heat sink you have installed in this amp….
Kumazawa: As matter of fact, the larger a semiconductor device is, the slower its recovery time will be. Since a sense of speed and rapid rise are essential to good sound quality, it is best to use components that are no larger than they need to be. That’s why we didn’t select parts with more capacity than was essential.
— Really? That is a surprise. So that is why you are using a heat sink to disperse excess heat.
Kumazawa: When it comes to the power transformer or block capacitors, extra capacity is a good thing. But this does not necessary also hold true for semiconductor devices.
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Constant-current regulators to help “push out” the sound
— I understand that you also used a new type of power supply circuitry for the preamplifier block.
Kumazawa: Yes, we employed discrete constant-current power supply blocks for enhanced stability. There are separate core power supplies for the preamplifier block, DAC block, and DSP block.
— I see, local regulators provide separate power supplies to the different sections. This sort of functionality is normally provided using three-pin IC regulators, right?
Kumazawa: Yes, exactly. IC regulators do actually have their advantages. For example, they provide excellent load following in circuits where the load varies suddenly. However, the constant-current regulators used in the RX-V2600 operate without feedback. So long as the load is constant they deliver a stable supply of current and produce little noise. In that sense I think they contribute to improved sound quality. The characteristics of the two types of power supplies differ, so in the RX-V2600 we use IC regulators for some sections and new constant-current regulators for others to best match their individual properties.
— I see. Now, what sort of effect on the sound does using these constant-current regulators make?
Kumazawa: In concrete terms, they make the sound seem to be “pushed out” with more force. The bass drum and string basses have an increased sense of fullness and release and seem more forward and powerful to the listener. Vocals have a greater fullness. The things I am describing are something you will recognize as different the moment you actually hear them.
— Are these circuit enhancements something you just happened to stumble across by chance?
Kumazawa: Not really. In fact, we were discussing these sorts of things in the final stage of development of the RX-V2500. We can say that the issues we were struggling with then have been solved in the new RX-V2600. At Yamaha groups of several engineers work together to improve sound quality—I believe we talked about this when the RX-V2500 came out. The engineers focus on things like ripple currents or high-frequency noise that can affect the sound. They use analysers to measure and digitise the phenomena they are dealing with and then develop methods to realize improvements.
— It is easy to lose sight of the importance of such aspects.
Kumazawa: This is something that we ourselves need to reflect on in some respects. If we think of tweaking the sound quality as some sort of art that only exceptionally talented people can do and always talk about making things more “audio like” and what the hi-fi fanatics will think, well then we will never make much progress. (Laughs.)
— If we always look at things in cut and dried terms the efficiency is rather poor, right?
Kumazawa: I think that ideas such as our new constant-current regulators come about on the basis of objective judgments of the effects of measured values on the sound, rather than simply through the skills of individuals.
5
Low-jitter PLL for fundamentally improved digital signal accuracy
— Next, I’d like to ask you about another one of the key parts of the RX-V2600, the DAC block.
Kumazawa: In the RX-V2600 we used Burr-Brown DACs for all channels. Some will say “Not again!”, however, we chose Burr-Brown DACs not just for the brand name, but because they really do have better sound quality. They also provide good sonic positioning in the low range. Also, I like the sound in the high range to have a natural feel, rather than a sharp, pinched one. By using the same DAC devices for all channels we have managed to achieve a wonderful sonic cohesiveness when reproducing multi-channel material.
— You also used Burr-Brown op-amps, I believe.
Kumazawa: Yes, that’s right. In the RX-V2600 we used Burr-Brown op-amps for the buffer amplifiers downstream of the DACs. Naturally, they have the same sonic tendencies as the DACs. They make possible the expression of high-quality hi-fi sound with plenty of depth.
— What about the circuitry?
Kumazawa: Recently, in the audio world, there has been a renewed focus on the effects of jitter in the digital signal on the sound quality. The RX-V2600 has a new circuit design that takes a simple approach to improving jitter characteristics. At Yamaha we’re calling it the Low Jitter PLL Circuit.
— Does it involve something like the use of a more accurate internal clock oscillator?
Kumazawa: No, it’s not like that. Simply put, it is a circuit design that is fundamentally not very susceptible to jitter contained in the input signal. Not just the RX-V2600 but all receivers that handle digital signals have a circuit called a digital interface receiver (DIR) that accepts the digital input, generates a clock, and sends it to the DAC. A phase-locked loop (PLL) is used to generate the clock, and by switching its time constant at the point when the signal begins to be received it is possible to minimize the effects of any jitter components the input signal may contain.
— In other words, you are making the amp circuitry’s responsiveness to the input signal somewhat sluggish.
Kumazawa: Well, yes, in a way. Jitter refers to fluctuations along the time axis of the signal. Lowering responsiveness therefore reduces its effects. But if the responsiveness is slow from the start it may be difficult to lock onto the signal when it is first received or if the digital cable is unplugged and then reinserted. It is therefore essential to lock onto the signal when it is first received and to switch to a more sluggish PLL time constant only after the clock has stabilized. There are a variety of technological means for reducing jitter. For example, among Hi-Fi fanatics there has recently been a lot of interest in regenerating the clock using an ultra-precise resonator made of rubidium, or the like. Nevertheless, the digital signal comes from an external source, and its accuracy is therefore dependent on external factors. We feel that it is much more effective to try to eliminate the effects of these external factors, rather than spending a lot of money on exotic resonators.
— That sounds both smart and practical. However, when we look at the audio board we can see that there is still a mixture of various devices, such as electrolytic capacitors. Is this the result of sound quality tweaking?
Kumazawa: I suppose what you want to say is that in addition to the gold high-sound-quality capacitors there are also some regular black ones mixed in. (Laughs.) As I always say, using too many so-called “audiophile parts” can be counterproductive. For example, in terms of the RX-V2600, using all high-sound-quality capacitors really would make for a more “high-quality” sound, but the sonic image would be too centred and the amp would be fatiguing to listen to after a certain period of time. This is why it is important also to use normal parts to ensure a balanced sound. Naturally, we do sometimes create custom made parts for specific sonic effects. For example, this copper earth point gave us very good results when we tested it in prototype, so we had it custom made for use in the RX-V2600. In the end tweaking the sound is not about individual parts. Rather, it involves efforts to improve the basis for the overall circuit design.
6
Freedom to select from all types of video sources
Digital Video
At last, full video conversion
— Next I would like to ask Mr. Suzuki to tell us about the video circuitry of the RX-V2600. It would seem that your putting true digital video conversion capabilities into an A/V receiver in this price range has created quite a stir.
Suzuki: Yes. Digital video conversion and HDMI compatibility are the two big video related features of the RX-V2600. With conventional analogue video conversion not all types of input signals could be output, and in particular there were limitations in the area of down-conversion. As for the GUI and other on-screen display features, the types of terminals these could be output to with conventional analogue circuitry were limited, and as a result the picture would be interrupted every time the display was switched on or off. These sorts of inconveniences have been completely eliminated in the RX-V2600.
Full HDMI support for analogue sources as well
— So it is now possible to output analogue video signals from the HDMI terminal.
Suzuki: Yes, that’s right. Even though HDMI has the advantage of allowing connections to the display using a single cable, with conventional analogue sources it was still necessary to connect separate audio and video cables. The RX-V2600 also has built in IP conversion, so interlaced input signals can be output as progressive signals. This applies mainly to projectors, but under the HDMI display standard progressive input is standard and interlaced input is optional. The up-converted 480i signal cannot be used as-is by some video components because they only accept 480p and above. But with the RX-V2600 basically any display and any input signal are okay. You could say that this provides consumers with confidence for the future.
— This is a feature people really want when you consider the constant advances in video equipment. Another thing that surprised me is that the RX-V2600 has the capability to upscale 480i and 480p signals to1080i or 720p. A feature like this seems like a real luxury in an A/V receiver costing less than £1000.
Suzuki: I agree. This function is called high-definition video upscaling, and it is a feature we are really proud of. It allows you to take an analogue input signal and output it via the HDMI as a 720p or 1080i signal. It gives new life to existing video resources by turning them into high-definition video signals. This feature will probably be most appreciated by veteran cinema buffs.
— This is a feature that has previously been available only on a few high-end components, and the devices are still expensive. It must have been a real challenge to design a feature such as this in this price range.
Suzuki: I suppose you have a point there. It is true that the necessary devices are expensive, and the main function of an A/V receiver is still audio, after all. (Laughs.) Nevertheless, we feel that this is a feature that consumers will consider to be an essential one in the years ahead. That’s why we went ahead and put it into the RX-V2600 as a key function.
— The video board is large and looks like it is equipped with important functions. How does the picture quality of the RX-V2600 compare with earlier analogue AV amps?
Suzuki: The main prerequisite for A/V receiver video circuitry is that it does not degrade the quality of the input signal. This is why we do not try to build in “image enhancing” functions. Naturally, however, we have built up considerable know-how in the area of maintaining signal quality. It is of course essential to use devices of good provenance, and that is why we have chosen devices such as high-performance video encoders from the well-known company Analog Devices Inc. Also, to prevent signal degradation, in past AV receivers and in the RX-V2600 as well we have used board-to-board direct connectors for connecting wiring boards. Finally, as part of the video conversion process, the analogue signal passes through a Time Base Corrector. This suppresses instability even in degraded signals and provides better video reproduction.
7
Assuring connection compatibility
HDMI
HDMI connections assure compatibility
— Mr. Yoshizawa, you were mainly responsible for supervising development of the HDMI control software. What did your job consist of, specifically?
Yoshizawa: The area I was responsible for was assuring mutual compatibility between the RX-V2600 and other HDMI devices connected to it. The HDMI specifications are laid down in a standard, but if you actually go and connect some of the DVD players and displays now on the market, you will find that some of them exhibit what we might call eccentricities in their behaviour. There are cases where they operate in unexpected ways in some minor details. This is why it was necessary to verify that any HDMI component on the market could be connected and work without problems and, where necessary, to make improvements to the control functions of the RX-V2600.
— So providing support for a new format involves more than just adding an extra terminal. You have to deal with other issues such as you have just described. How specifically do you go about verifying compatibility?
Yoshizawa: You go out and buy a whole lot of HDMI components, then you check them one by one.
— That sounds like quite a big job. You have to go out and actually buy them? How many do you have to purchase all together?
Yoshizawa: Some of the components are lent to us by other departments or our overseas organisations, but basically we have to purchase most of them. I never actually took a count, but the number is pretty large because we try to cover all of the product categories as far as possible.
— You must come across some pretty awful ones. (Laughs.)
Yoshizawa: Well, let’s just say that some of them do not operate entirely in conformity with the specifications. Nevertheless, we try to make up for such deficiencies whenever we can.
— So you expand the tolerances to match the actual status of the products on the market?
Yoshizawa: Yes, that’s right. That is what we are in fact doing. An A/V receiver is a component in between the player and the display, so the difficulty we face is the need to widen the tolerances for the input as far as possible and to be as strict as possible with the tolerances for the output. Lenient with input signals, strict with output signals
Maegaki: For example, if input and output matched exactly, as if the player were connected directly to the display, a certain amount of allowance would exist. But an A/V receiver must try to output a signal that the display can accept, even if there is something a little out of order with the input signal. At the same time, the A/V receiver must retain the quality level of the original input signal. Otherwise, if for example the user can connect the player directly to the display and see a picture, but no picture is visible when the signal is routed through the A/V receiver, the receiver would be inadequate.
— I see. It all seems very difficult. No one takes responsibility for ensuring compatibility, so it ends up being up to each individual manufacturer then?
Suzuki: There really is no single body that takes responsibility for maintaining compatibility. (Laughs.) There is an industry-wide event called Plug Fest held every two years, with the Consumer Electronics Association and Digital Content Protection, LCC (the organization that set HDCP standards) playing the central role. Companies bring their products to this event and try connecting them to each other. In addition to products such as receivers and players, there are also giant plasma TVs and the like.
—Plug Fest? It sounds like fun. (Laughs.) Does everyone gang up on manufacturers who bring non-standard products to the event and give them what for?
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Suzuki: Nothing quite like that happens. Many of the models companies bring are still in development, so it is expected that there will be some problems. Compatibility is a frequent issue in the marketplace, and the goal of Plug Fest is to minimize such problems as far as possible. We all work together to identify issues before they reach the market and come up with solutions for them.
— I see. Incidentally, what are the areas where it is difficult to achieve compatibility, and what are the results?
Suzuki: When you connect HDMI components, there is a copyright protection standard called HDCP that operates in addition to the HDMI standard. These two standards are completely separate, and HDCP uses stricter timing authentication than HDMI. This means that different authentication processing methods must be used in cases where the player is connected directly to the display and in cases where they are connected via a repeater, such as a receiver.
— Really!
Suzuki: What’s more, an A/V receiver, for example, acts as a transmitter, connected one-on-one to the display, when there is no input signal. Once a player is connected, however, the A/V receiver must function as a repeater.
— I see.
Suzuki: In other words, the A/V receiver must change operating modes depending on what sort of component or components it is connected to. The timing of this switchover can determine whether or not those components function properly. This is why we have to fine tune the timing of switching operations and the like.
— Are you able to solve these problems through software programming?
Suzuki: Yes, that’s right.
— Things are much more complex than they seem! Though saying “HDMI compatibility” sounds simple, it involves much more than just adding input and output terminals. You also have to make allowances for each individual connection type.
Suzuki: It would be a relatively simple matter if, for example, all we had to do was to ensure compatibility with some standard reference component. But we have to make sure our product works with all the different components actually out there, and that is where the difficulty lies.
[small]Отредактировано: 22-02-2006, 20:34[/small]
