RE: [midatlanticretro] Partially OT: WAV file processing question
Re: [midatlanticretro] Partially OT: WAV file processing questionAh. I am most interested in the tape2wav part, producing good copy-able wavs that can be used as masters for reproduction.
From: Richard A. Cini <rcini@...>
Sent: Tuesday, November 25, 2008 9:37 PM
To: email@example.com <firstname.lastname@example.org>
Subject: Re: [midatlanticretro] Partially OT: WAV file processing question
I dont doubt that a studio-level program could do this, but the challenge is that people who use the emulator would have to send me the raw dumps and Id have to make them usable. If I build this capability programmability, then Altair32 users can open the WAV file directly. Thats really what Im striving for (at least for now :-))
On 11/25/08 9:17 PM, "B Degnan" <billdeg@...> wrote:
Richard A. Cini wrote:
Re: [midatlanticretro] Partially OT: WAV file processing question Guys:
I did some research today. I would prefer working directly with sound card samples only because thats how most normal people are going to produce WAV files (not that youre not normal Bill...). Its easy to strip the WAV header using a program called Wav2Pcm (code available in the ether). There is something called a Goertzel transform which is a modified FFT whose purpose is to zero-in on a specific frequency. If I couple that with a type of a bandpass filter, I think I can tease out the 1850Hz and 2400Hz signals which represent logic 0 and 1, respectively.
The tape sample I have is 8-bit mono at 11.025kHz, but most of the other sample stuff Im working with is 16-bit mono at 44.1kHz.
Recording Studio software can do all of this easily. Some of them let you write your own filters, mastering by using threshholds, etc.
Jumping OT slightly:
Here is an intersting article
Sort of a wah wah pedal for cassette signal processing that mimic teletype outputs and compresses the sound signal. The compression clarifies the zero one difference.
Collector of Classic Computers
Build Master and lead engineer, Altair32 Emulator
- I took Pascal in college but it has been about 15 years since I have used it. I might be able to help with the Pascal. I do have books on Pascal if you want to borrow them. Let me know.----- Original Message -----From: Jim ScheefSent: Tuesday, November 25, 2008 2:49 PMSubject: Re: [midatlanticretro] Partially OT: WAV file processing question
Rich and Bill,
This is an interesting project. From a programming standpoint on a PC
maybe it would be good to write a program that can read and process a
standard WAV file but swallow the header and trailer info in the WAV and
just pass on the data part to the "Altair". The reverse might be useful
as well - to accept the data sounds and output a standard WAV.
Rich, Pascal is obtuse because the code is "upside down". Pascal
requires that a subroutine be defined before it can be referenced.
Pretend the code is VB but read each section starting at the bottom of
the listing (where program flow actually begins) and it will make more
Bill Degnan wrote:
> > Richard A. Cini wrote:
> > > All:
> > >
> > > I've been asked to add direct support for WAV file images of real
> > > Altair cassette tapes in the Altair32 Emulator. Essentially a WAV
> > > file, minus the header, is a series of numbers that represent the
> > > sample. Since the sample is 8-bit monaural, each sample is just one
> > > byte. The sampling frequency is 22.050kHz. The recording is 124
> > > seconds long, so there are about 2.7 million samples. The 88-ACR used
> > > a 2400Hz/1850Hz tone pair to represent logic 1 and 0, respectively. In
> > > the end, I need to turn these samples into live bits and bytes.
> > >
> > > I'm not exactly sure where to start with this programming project. Has
> > > anyone on-list ever done this kind of software audio processing?
> > > Basically the audio segment of the board has some signal conditioning
> > > and an XR210 FSK demodulator.
> > >
> > > Any help would be appreciated. Thanks.
> > >
> I plan to work on this project independently, from a sound engineer
> perspective. I will let you know how it goes. I could be wrong, but I
> believe it's more the levels/mix than the sample rate. There is nothing
> wrong with over-sampling the sound source. The master of any program on
> tape was usually a record album. I wonder if the original BASIC record
> albums exist.