Is PASC the same as mp1?

Technology
21

What Max said. When you go through the TOSlink (or Coax, same thing) to record digital audio from a PC (Mac, Arduino, whatever), the format is PCM, i.e. uncompressed Pulse Code Modulation. The internal PASC compressor of the recorder encodes it to PASC and records the PASC onto tape. So there’s no point in encoding the music in PASC before you do that; it has to be decoded to PCM while you do the transfer anyway.

If you want to record audio files from your PC to a DCC recorder and you don’t have a DCC-175 with PC-cable, you get the best quality by using as few conversions as possible. If you have a choice when you source(*) your audio files, start with the highest quality possible, e.g. WAV (uncompressed) or a lossless compression format (e.g. FLAC). Set your output to PCM stereo, using the same sample frequency as your file if possible. If your file has a higher sample frequency than 48 kHz, use either 44.1 or 48kHz, the best choice is the one that divides most evenly into the sample frequency of your file.

Connect your recorder to a digital output via Coax or Toslink (the bits on each of those two are formatted exactly the same so there’s no reason to choose one over the other). The play the audio file to that output at full volume. Sorry I don’t have a recommendation for good software (if anyone does, please chime in).

Most files with music are 16 bits. Those files will sound just fine if you record them to any DCC recorder. If your file has more bits (18 or 20 or 24 or whatever), an 18-bit recorder or 20-bit recorder will process the extra bits too if the SPDIF output of your PC supports them.

===Jac

(*) Source=grabbing files from audio CD or downloading them from the Internet. DRM-protected digital audio files can probably be recorded to DCC by playing them to a digital output device, including HDMI to DVI+SPDIF converters.

1 Like
22

Thanks Max, thanks Jac for the detailed explanation.
I have different intention with DCC. Basically copy the vinyl collection by the following method.

  1. Phono preamp out → DCC analog input
  2. Play pre recorded dcc cassettes. I have very few, the ones in eBay Germany are very expensive.

Does a separate PASC encoder gives better results than the built-in encoders of DCC machines? I have DCC 951, 900 and a DCC 300.

23

Phono preamp to analog in should work great. The DCC recorder manuals recommend keeping the average audio level around -9 dB to prevent clipping.

Copying a DCC from one recorder to another via digital should work great too. However your copy won’t have song titles and it won’t be possible to copy the copy again without an SCMS defeater.

I don’t know how or why you would use a separate PASC encoder in either of those cases.

=== Jac

1 Like
24

For the same reason as some people use seperate DA converters in their cd players I guess.

But as far as I know there is no such thing.
Would be pointless unless one could plug in the Pasc signal directly in the write amplifier… and how the hell do you stream that? Through toslink it would be decompressed into pcm and than to pasc again…
Am I right?

25

First time it didn’t compute…
That is not a small thing!
Is that the reason why these recordings sound so well?

26

But… that is the thing isn’t it? I’m slow I know… but if we somehow know how to put the pasc/mp1 signal devided the proper way in to the heads we have arrived??? For duplicating new releases…
DccMuseum could use standard recorders in much higher quantities than now with the 175…
And use windows 10 and an interface… using usb??? I only wish that I had the knowledge but I think there is something here…

27

The PASC signal doesn’t go into the write amplifier(*) but I understand what you’re saying.

As I mentioned, every recorder has an i2s bus with the PASC signal. It’s very well documented how the data goes over that bus and it’s not that difficult (theoretically) to inject your own PASC data. In practice, however, there are some roadblocks that make it difficult to do that: when recording, the PASC encoder provides the PASC signal on the bus, and you would have to disconnect the encoder to put your own signal. But while you do this, your bits have to be in sync with the clock signals generated by the PASC encoder. It’s not impossible, it’s just not as easy as plugging something in the back of the machine.

Streaming i2s over long distances is difficult. The i2s protocol is intended for short distance communication, e.g. within a DCC recorder. So the best way to do it would probably be to use a microcontroller that supports i2s slave mode, for example a Teensy 3.x or 4.x, or a Raspberry Pi. You would also need some logic to connect/disconnect the chip that normally puts the signal on the bus (or you would need two i2s connections but I won’t go into that). You could use an SD card or a USB connection from a PC to store or stream the music.

It gets complicated really fast, and I’m working on doing something like this, but for most users it’s probably easier to just connect the PC to the recorder via coax or TOSlink and use the PASC encoder in the recorder.

Ha! I like to think it is. But really, the sound quality is 99.9% because Ben Liebrand supplied excellent quality 96kHz 24bit master files. The remaining 0.1% is due to the fact that apparently I know what I’m doing, well enough to transfer those masters to MP1, then to the DCC-studio program format. And DCC-studio simply copied it to the tapes.

That’s basically what we do for our releases at the DCC Museum.

But we want to go further in the future. The cassettes we’ve made so far are all made by consumer recorders so they’re not formatted as prerecorded cassettes. If we make a cassette with (say) 10 tracks and you tell the recorder to go from track 1 to track 10, it’s going to wind the entire tape forward to the end of side A, then back to almost the beginning of side B, whereas on a prerecorded tape, the recorder would already know that if it needs to go from track 1 to 10, it only needs to reverse and then maybe wind for a few seconds.

We have the information to accomplish that (again, theoretically), but we would need to inject not only the audio, but also the SYSINFO and AUXINFO data while the tapes are being recorded, and we need software to correctly format the information of course. It’s going to be a while before we can do that, but I’m making some progress.

I would love make it possible to modify existing decks to do fully automated recording of cassettes from an SD card or a streaming computer via USB. It would be even more awesome if we could make an automatic cassette changer for this purpose (maybe using Lego or FischerTechnik), so that nobody has to stay in the room to do the boring part of recording the cassettes, and so that we don’t need the DCC-175’s and some old unstable Windows 98 computers.

=== Jac

(*) If you must know: before the PASC data goes on tape, the recorder adds SYSINFO and AUXINFO, then adds error detection/correction data, modulates the data with 8-to-10 modulation, then interleaves the 8 main data tracks on the tape. The write amplifiers are just that: write amps. Simply sending PASC data won’t work.

28

You are well beyond me… I’ve got loads of reading to do…

29

You are not lying @Jac
Last couple of weeks I’ve been studying… all I say is that this system is awesome… it took less to put people on the moon! (Sorry Neil, you did a great job!)