Data Stream Dissector (DSD) Kit User's Guide last revised 12/31/93 Introduction ------------ This document describes how to use the DSD. It begins with a concise definition of all the inputs, outputs, indicators, and controls. It then describes the controls in greater detail and explains a bit about the digital audio protocols. Background ---------- The DSD processes signals conforming to the IEC-958 standard. These are more commonly called "S/PDIF". There are 2 flavors of IEC-958: an electrical interface which uses 75 ohm coaxial cable and RCA "phono" connectors, and an optical interface, which use fiber-optic cable and Toslink connectors. Both flavors use the same data formats. In this document, we will use the terms "coax" and "opto" and when we say "IEC-958", we mean either one. There is an emerging de facto standard that uses AT&T ST type optical connectors for IEC-958. This is an expensive arrangement. The ST opto is not supported by the DSD. IEC-958 is considered the "consumer" digital audio format. There is a "pro" counterpart, AES3-1985, commonly called "AES/EBU". Much of the data format is the same, some of it is different, the signaling is different, and the connectors are different. The DSD does not support AES3-1985. Data Stream Dissector (DSD) Kit User's Guide (page 2 of 8) Inputs ------ The DSD has up to 4 IEC-958 inputs. Of those 4 inputs, up to 4 can be configured for coax and up to 2 can be configured for opto. The DSD kit comes configured for, and with parts for, 3 coax and 1 opto. Of the 3 coax inputs, #0 and #1 are transformer coupled and #2 is capacitor coupled. The transformer is perhaps overkill and we wanted to be able to try both approaches. Please let the DSD designers know if you have more or less trouble with the transformer or capacitor coupled. What we would "like" to hear, is that your system is less susceptible to electromagnetic interference when using the transformer coupled inputs. Table 1. Inputs Input Type Coupling ----- ---- ----------- #0 Coax Transformer #1 Coax Transformer #2 Coax Capacitor #3 Opto Optical Aside from coax/opto difference and coupling differences, all 4 inputs should be equivalent. They are selected by the input selection controls, described below. Connect up to 4 digital audio sources (such as CD players, DAT decks, PCM converters, computers) to the DSD. For coax connections always use 75 ohm cables. Outputs ------- The DSD has up to 4 coax outputs and up to 2 opto outputs. The DSD kit comes with enough parts for 3 coax outputs and 1 opto output. All 4 coax outputs are transformer coupled. All outputs are active all the time. There is no need to select between them. There is no correspondence what-so-ever between input #1 and output #1 and so forth. Connect up to 6 digital audio sinks (such as DAT decks, PCM converters, computers) to the DSD. Data Stream Dissector (DSD) Kit User's Guide (page 3 of 8) Indicators ---------- The DSD has 4 indicator LEDs (light emitting diodes). Table 2 describes their functions: Table 2. Indicators Ref. Number Color Signal Meaning ------ ------ ------ -------------------------------------- D1 Red FC1 Indicates the sample rate, as shown in Table 2A. D2 Red FC0 Indicates the sample rate, as shown in Table 2A. D3 Yellow C3* When ON, the data stream does not have the Emphasis flag set. When OFF, the data stream has the Emphasis flag set. D4 Green ERF* When ON, the DSD is locked on to the input signal. When OFF, there is an error condition or there is no input present. D1, D2, and D3 are provided for informational purposes only. You need not react to them. D4 is important, though. It means "All Systems Go". There's practically no way the DSD will work if D4 does not light up. Table 2A. Sample Rate Indications D1 D2 Rate --- --- -------- OFF OFF 44.1 kHz OFF ON 48 kHz ON OFF 32 kHz Data Stream Dissector (DSD) Kit User's Guide (page 4 of 8) Control Overview ---------------- The DSD contains circuitry that automatically sets the sample rate and emphasis. Thus, the only switches that you will normally need to use are the input selection switches. Everything else should be set and forget. But you will need to familiarize yourself with all of them. The DSD has 10 switches for you to play with. The basic kit has these all on 1 DIP-switch. Your DSD may have some combination of panel mounted toggle switches and/or a rotary switch. In any case, I will refer to the switches according to their numbers on the 10-position DIP-switch, S1-S10. In Table 3, below, the input numbers refer to those explained in Table 1, above. Note that the switch numbers do not match the input numbers (tough). The rest of the table is explained in the sections that follow. Table 3. Switches Switch ON (Closed) OFF (Open) ------ ------------- ------------- S1 Bypass Don't Bypass S2 Select In #3 (see below) S3 Select In #2 (see below) S4 Select In #1 (see below) S5 Select In #0 (see below) S6 Set C8 bit Clear C8 bit S7 Set C15 bit Clear C15 bit S8 Set C9 bit Clear C9 bit S9 Clear U bits Pass U bits S10 Set C2 bit Clear C2 bit If you are anxious to try your DSD out, set S1, S2, S3, S4, S5, and S9 to OFF; set S6, S7, S8, and S10 to ON, and use Input #0. If you want to know why, keep reading. Data Stream Dissector (DSD) Kit User's Guide (page 5 of 8) Input Selection --------------- WARNING: If you have a digital audio device hooked up with input *and* output going to the DSD, and it is in *record* mode or some other mode that feeds the input to output, and this input is selected on the DSD, a feedback loop will be created which will be horribly noisy and possibly destructive. For example, if you have a DAT deck with digital output connected to input #1 and digital input connected to any DSD output, and this deck is also set to record from digital input, and the DSD is set to input #1, you're hosed. The input selection logic uses a priority scheme. To put it simply, the highest numbered switch that is ON, gets the priority, and selects its input. To put it complicatedly, see Table 4. Table 4. Input Selection switches ----------------------------- selected S2 S3 S4 S5 input ----- ----- ----- ----- -------- OFF OFF OFF OFF #0 don't don't don't ON #0 care care care don't don't ON OFF #1 care care don't ON OFF OFF #2 care ON OFF OFF OFF #3 Data Stream Dissector (DSD) Kit User's Guide (page 6 of 8) Bypass Mode ----------- When we designed the DSD, we figured that you would probably keep it in your digital audio dubbing chain all the time, since it would not hurt anything, and it makes a convenient switcher/distributor. But being the anal types that we are, we put in a Bypass mode. When Bypass (switch S1) is ON, the Crystal Semiconductor digital audio receiver and transmitter are bypassed. The opto and coax line receiver and line driver and switching logic are still used, though. In bypass mode, the input digital audio stream flows from the selected input to all outputs unaltered. This feature is particularly handy for source tapes which already have the desired C Bits and U Bits (see below). Also, if you are having difficulties getting a lock on a particular deck or tape or are experiencing some sort of sun spot or solar flare, try the Bypass mode. Subcode ------- The IEC-958 specification dedicates certain parts of the digital audio stream to be subcode. The subcode that carries useful, non-audio information consists of the "C bits" and the "U bits". When in Bypass mode, the DSD passes C bits and U bits from input to output. When not in Bypass mode, the DSD uses incoming C bits to determine the sample rate and emphasis of the incoming signal. It then generates a new set of C bits for the output, using the sample rate and emphasis it got from the input, and using the values you supply for 4 of the other C bits, which are discussed later. Also, when not in Bypass mode, the DSD gives you a choice of passing the U bits from input to output are completely discarding them. This is discussed in the following section. Data Stream Dissector (DSD) Kit User's Guide (page 7 of 8) U Bits ------ We never quite figured out what the protocol for U bits was. It does not matter much: to do anything really useful with them would require a great deal of additional circuitry. As far as we know, everything will work fine if we clear all the U bits, by setting switch S9 to ON, which has the side effect that IDs (start, skip, end) will not get passed from input to output. This can be very useful if the source tape has extraneous start IDs. This can be necessary when the source is a CD. Under most circumstances, you should be able to turn off S9 and pass the U bits (and therefore the source tape IDs). If you would prefer to not pass the IDs from the source tape, or have problems with extraneous IDs at the destination deck, try turning S9 ON. C Bits ------ Switches S6, S7, S8, and S10 control the values of bits C8, C15, C9, and C2, respectively, in the channel status block of the outgoing digital audio signal. C8 and C9 are the two most significant bits of the 7-bit Category Code. The other 5 bits are permanently set to 0. It works out that we can get just about any category code we want this way. Table 5 is a simplification of category codes. Table 5. Category Codes C bits Switches ------------ ------------ C9 C8 S8 S6 Category ---- ---- ---- ---- ------------------ 0 0 OFF OFF General 0 1 OFF ON PCM, and others 1 0 ON OFF CD 1 1 ON ON DAT We put these switches in for flexibility and experimentation. For most applications, you will want to set the category code to "DAT" (both switches ON), even if the original source was not DAT. That is because the "General" and "PCM" categories are considered "Ignorant" categories. This is with respect to C15, described below. To put it simply, if you record a tape with an Ignorant category, then some DAT decks will ignore the input C15 bit and default to a C15 bit which may not be the one you wanted. Data Stream Dissector (DSD) Kit User's Guide (page 8 of 8) C Bits (continued) ------------------ C2 is the Copy/Copyright bit. C15 is the Generation Status bit. Together, C2 and C15 make up the Serial Copy Management System (SCMS) bits. The user may be, under certain circumstances and in certain countries, legally obligated to set the SCMS bits correctly. When the user owns the rights to the digital audio in question, the user may set the SCMS bits to the level of copy protection desired. The various combinations of C2 and C15 are detailed in Table 6. Table 6. SCMS Codes C bits Switches ------------ ------------ Categ. SCMS C2 C15 S10 S7 Code Code Meaning ---- ---- ---- ---- ------ ---- --------------- 0 0 OFF OFF General 11 Restricted 0 0 OFF OFF PCM 10 Prohibited 0 0 OFF OFF CD 11 Restricted 0 0 OFF OFF DAT 10 Prohibited 0 1 OFF ON General 10 Prohibited 0 1 OFF ON PCM 11 Restricted 0 1 OFF ON CD 10 Prohibited 0 1 OFF ON DAT 11 Restricted 1 0 ON OFF all 00 Unrestricted 1 1 ON ON all 00 Unrestricted As the table shows, the interpretation of C15 depends on the category code. Refer to IEC-958 for a complete explanation of these codes. There are several other C Bits which are set automatically by the DSD. They are described in Table 7. This information is provided for reference only. Table 7. Other C Bits. C Bit Meaning Setting ------- --------------- ----------------------- C0 pro/consumer set to consumer C1 audio/non-audio set to audio C3 emphasis depends on input stream C4-C7 reserved set to 0 C10-C14 more categories set to 0 C16-C31 reserved set to 0 C32-C33 frequency depends on input stream C34-end reserved set to 0 -----------------------------------------------------------------------