Guralp Systems Limited
Section Index: 5.1 Recording 5.2 Files 5.3 Playback

Chapter 5. Recording and playback

Scream! allows you to record all incoming data and store it on the local hard disk. To do this, you should select the streams you want to record from Scream!'s main window, right-click, and choose Start recording from the pop-up menu. The streams will display Yes in the Rec. column to indicate that they are recording.

When Scream! starts recording, it starts at the earliest point in the current stream buffer, and immediately records all it can. For continuous streams, the recorder will soon catch up with the real-time data.

By default, recorded data is placed in a data directory within the Scream 4 installation, in GCF format. Scream! records files for each stream separately, which it puts in that stream's own directory. This directory may contain one or several GCF files.

Scream! has a number of options which allow you to change the way data is recorded and filed. From the main window, select Setup… from the File menu to open the Setup window. Click on the Recording tab. (Scream!'s setup window also provides a number of other kinds of options. Consult Scream!'s documentation or online help for more details.)

5.1 Recording


The upper part of this pane allows you to instruct Scream! to record various streams automatically. Scream! will start recording all relevant streams immediately, but will also remember the settings for the next time it is started up.

Auto Record—Enable for Data Streams causes all local data streams to be saved automatically, whilst Auto Record—Enable for Status Streams does the same for digitizer status streams (those ending in 00.)

Auto-upload on heartbeat : If a digitizer has been configured to record data into its own Flash memory only (FILING mode), it transmits heartbeat status messages. With this box checked, Scream! will listen for heartbeat messages, and ask the digitizer to send filed data whenever it receives one.

Auto-record uploaded streams : If you have selected Auto-upload on heartbeat, you can check this box to instruct Scream! to automatically record to the local hard disk any data that it receives. These are not normally counted with the streams above, since they may come from another Scream! which is already recording.

The lower section tells Scream! how to use its hard disk space:

If there is very little space on the disk, the PC's operating system can become slow or unstable. By default, Scream! will consider the disk “full” when only 50 Mb of space remains on it. You can change this amount by altering the value at bottom right.

5.2 Files

Another part of the Setup window allows you to alter the way Scream! files the data it receives. Click on the Files tab to open the following pane:


The options you can change are:

Base Directory: This specifies the root directory in which data files will be saved. Files for each stream are stored in sub-directories off this root. The sub-directory structure depends on the filename format.

Filename format: This allows you to describe how you want files to be named by entering a format specifier. The string you enter is used to construct the file names for all files. Among the specifiers you can use are:

YYYY the year number (e.g. 2003),

M the month number (1 – 12),

D the day of the month (1 – 31),

H the hour (0 – 23),

N the minute (0 – 59),

S the second (0 – 59),

R or J the day in the year (0 – 366),

X the date represented as an 8-digit hexadecimal number (this allows a complete date to fit in the DOS 8.3 format, for compatibility),

I the System ID,

T the Stream ID (e.g. DM24Z2),

C the component identifier (Z,N,E,M, etc.),

P the sample rate, in samples per second;

A the name of the stream, if you have set a mapping, otherwise the same as T.

The specifiers MM, DD, HH, NN, SS, RRR, JJJ, IIIIII and TTTTTT are the same as their single-letter counterparts, but they are padded with zeros or underscores to a constant length. YY can also be used for a 2-digit abbreviation of the year (e.g. 03 for 2003), and MMM for a 3-letter month name (jan, feb, etc.)

Any other letters (including small letters) in the filename will be left as they are, so you can add constant descriptions or field separators as you wish. Owing to operating system limitations, you cannot use any of the punctuation marks * ? " : < > | in filenames. You can create directory structures by using the \ character.

For example:

T\YYYY_MM_DD;HHhNNmSSs will give filenames like dmz2\1997_10_05;07h35m20s.

You should always ensure that files are given unique names. Scream! writes each stream separately. If it finds that it cannot write to a file because it is already open for another stream, the write will fail and data will not be recorded.

Data Format: Selects the format of the recorded data files. Options are GCF, SAC, MiniSEED, P-SEGy, PEPP, SUDs, GSE, UFF (ufa and ufb; see below), and CSS. A single Scream! can only record in one format at a time.

Byte Order: For SAC, SEG-y, UFB and CSS files, the byte order of the files can be specified. This can be used to match the byte order with the native order of the platform where you are going to perform analysis. GCF and MiniSEED are defined to be in “Motorola or SPARC” byte order. PEPP and SUDs data is defined to be in “Intel” byte order. Byte order is not applicable to the ASCII-like GSE or UFA formats.

Granularity: Allows you to decide how large files are allowed to become before a new one is started, for three different types of stream (high sample rates, low sample rates and status streams). The distinction between high and low sample rates is set by the number in the Sample Rates >= box; the remaining boxes give the number of hours of data that Scream! should combine into a single file for each type of stream. In the example above, streams with a sample rate of 20 samples/sec or above will be recorded in files with up to 1 hour's data per file; lower-rate streams will be recorded in 4-hour files, whilst a new status file will be started every 12 hours. You will need to choose a Filename format (see above) which gives each file a unique name.

If you prefer to set a limit on a file's size, rather than its duration, choose Kilobytes from the drop-down menu (instead of Hours or Minutes) and set as appropriate.

Post-processor: This option allows you to specify a program which Scream! will run every time it closes a file. The name of the file is passed as a parameter. You can use this feature to interface to other analysis or archival systems, for example:

5.3 Playback

5.3.1  GCF files

To replay a stored GCF file or files: