How To Use SPL Graph

SPL Graph is a logging sound level and noise recorder. It is highly configurable to support many various use cases.

Audio/Video Settings

Time Delay Settings

Resolution Settings

Minimal Display

Homekit Integration

Remote Monitoring

Octave Logging

Ln Settings

Fast 50ms File Save Option

Other Settings

Notifications

Auto Save Setup

iCloud, Dropbox and File Exporting

Operating SPL Graph

This section describes how to operate SPL Graph. See the Settings section for information on how to set up SPL Graph for different use cases.

After you have set up the options that you wish to use, and selected the input source (if needed), you are ready to begin testing.

Starting and Stopping

Press the microphone icon Run / Stop button to start saving data. If you have turned on audio recording on the setup page, the audio will also be recorded. Press the Pause button (or any other button that would effect recording) and an alert message will be shown, allowing you to continue the measurement, pause, or stop it. If you select Pause, the measurment will proceed, but data points will not be recorded, and sounds occuring during pause will not be included in the measurement.

When there is a graph on the screen that also has recorded audio available (either from running a test or recalling a stored graph), the speaker icon Play / Stop button will let you play back the audio. In this mode, you can also swipe the cursor across the screen, to listen to a specific audio event.

Destructive Backspace

Tap the red left-curly arrow to delete the point at the cursor. Deleted points don't count in measurements. This button will only operate on recalled graphs, so that you can bring back the full data set if you delete too much.

Save / Recall

Tapping the square icon brings up the Save / Recall screen. Note that if you exit this module without explicitly saving the data, both the graph data and audio will be saved automatically in a temporary file, and can be recalled the next time that you open this module. This should also happen even if you exit the entire app by pressing the menu button on the device, or if the device runs out of battery, although this cannot be guaranteed.

Audio / Video Settings

You can record the actual audio as the test is running, either continuously or be events that exceed a preset threshold. Audio event records including a preroll of 10 seconds of audio before, and a postroll of 10 seconds of audio after the event. Video does not include a preroll, but does include a 10 second postroll.

Alternatively, you can choose to record video either continuously or by event. The video will also include the audio. Video recording is an optional feature, available as an in-app purchase.

Note that video recording will use up storage space on the iOS device more quickly than audio.

Audio files may be automatically copied to your iCloud or Dropbox, if enabled. (See below). Please note that Dropbox does not support storing video files for this app. We suggest migrating to or using iCloud if possible.

Capture None / Audio / Video

This switch allows you to select audio or video capture of the test. If the Event Recording field (see below) is empty, a recording of the entire test will be stored. Otherwise, only events above a preset SPL level will be captured.

Audio File Type

WAV stores an uncompressed 16-bit single channel wave file, typically at 48k. CAF stores an Apple CAF format file, which is about 1/4th the size of the WAV format file. M4A stores files using the Apple MPEG4 encoder, which results in files about 1/10th the size of WAV files.

Wave files consume about 5.8mb/minute (345 mb/hr). CAF files use about 1.6 mb/minute (86 mb/hour) of space on your device, and M4A files use about 36mb/hr. You will need a CAF converter if you are using a PC to listen the CAF file. Mac computers can play this format directly. M4A files should play directly on most systems.

Video Format Control

You can select different video resolutions, which change both the video resolution and the size of the files that are stored. Actual video resolution will vary depending on which device is being used, but typicall vary from 192x144 to 1920x1080.

Audio Monitor

Turn this on to route the input audio to the output path. Note that this may cause feedback if you are using the internal mic.

Gain Control

This slider lets you add gain to the playback audio volume. It does not have any affect on the recording, or on the video playback level.

Audio/Video Capture

SPL Graph can optionally record the audio or video while it is recording the sound level data. Select Audio or Video from the Audio / Video settings, and then select the format.

For Audio, WAV files are the largest, roughly 900mb/hour, CAF are about 200mb/hour, and M4A files are about 90mb/hour.

For video, the resolution choices and sizes vary by device.

If you want to conserve storage space, use the Notifications to set thresholds for recording audio. Video recording of events is not currently available.

Time Limits Settings

These settings affect when the measurement will start, and how long it will run.

Delay Start

Setting this value will result in a time delay before the graph (and audio recording, if enabled) begins.

Start at Next Hour

If turned on, the dealy time will be calculated at the start of the test to begin at the next even clock hour or minute. This can make reading the results in the XLS text file easier.

Run Limit

Setting this value causes the graph and audio recording to stop after the number of minutes in the field.

Resolution Settings

SPL Average (LEQ) per Graph Point

Select the resolution of the measurement, from 0.1 second to 60 minutes. This controls the amount of data that is stored per point on the screen. For example, if you choose 5 seconds, then 5 seconds of audio is averaged for each point plotted.

Note that if you select 0.1s, octave logging is disable for some iOS devices, as only the more recent iOS devices have enough processing speed do octave logging at that resolution.

When you select the resolution, the maximum time that can be stored for that resolution will be shown beneath the control.

This selectors define how long to average the SPL before drawing a new bar (and, creating a new data point). In effect, it also sets the minimum size of the LEQ. For example, when set to 1 second, a series of 1-second LEQs are computed and store. If you set it to 5s, you will get a series of 5-second LEQs. It also controls the maximum possible graph time: 1 second = 24 hours, 2 seconds = 48 hours, 5 seconds = 5 days, 10 seconds = 10 days.

Changing the Sec / Min  control changes the times that are available from the time selector.

Weighting (selected on main display screen)

The selected weighting is applied to the incoming audio. All values are computed taking the selected weighting into account.
Recording

Turn the recording switch on to enable audio recording while also plotting the SPL graph.

SPL Octave Logging Settings

Octave Logging

SPL octave and 1/3 octave logging is an option that must be purchased seperately from SPL Graph. To purchase this, tap the Info button that appears over the Octave Logging selector on the SPL Graph Setup page.

Octave Logging is powerful feature that allows logging the octave or 1/3 octave spectrum for every point that is saved in the SPL Graph. In octave or 1/3 octave logging mode, the overal LEQ for each band is shown on the screen, similarly to the RTA. You can also move the cursor back through the curve, and display the spectrum for any point in the graph. This spectrum display appears as dark lines, superimposed over the overall spectrum plot, which is blue.

In addition to storing the octave or 1/3 octave bands for every point, the unweighted SPL level, and A and C weighted levels are also captured. This means that you can select any of these options for the curve that is drawn, either while the test is running, or after a test is complete, or has been recalled from the Save / Recall screen.

When storing an octave or 1/3 octave band file, the overall Leq and Ln values are stored in the XLS file, for every band, and for the 3 weightings. You can optionally select to store all of the raw data for each graph point. This option appears on the Autosave screen.

Full Data Save

If this switch is turned off, a summary of the data will be recorded. If it is turned on, data for every point in the file will be saved. Note that if octave or 1/3 octave logging is turned on, this can cause a large file, up to several megabytes, to be saved.

Minimal Display Settings

The minimal display lets you present a simple display that shows only a single SPL dB numeric value, against a color background that reflects the level. When enabled, a smal "123" button will appear on the main screen, which switches the screen to the minimal display.

Enable

Turn this switch on to enable the minimal display.

Red, Yellow, Green Levels

Set the dB levels at which you would like the dispaly to change color.

Display Type

Select Fast or Slow to view the SPL as it would appear from a sound level meter set to Fast or Slow. Select LEQ to show the LEQ setup fields and view the SPL as an LEQ.

Main Screen

Turn this on to show the SPL reading on the main screen. This applies to the Fast or Slow setting only.

LEQ Time

Set the LEQ time average period to be used for the level testing.

LEQ Type Selector

Select LEQ Restarts to run conescutive LEQ tests. Select Running LEQ to choose a running LEQ for the test.

Homekit Integration

If you have Apple Homekit setup, you can link color light bulbs to the SPL color triggers in the Minimal Display. This allows you to have an external color light bulb as a notification for basic SPL level.

The colors will follow the SPL trigger settings in Minimal Display.

Remote Monitoring


Enabling this option will cause the app to transmit SPL data to cloud-based storage at the time interval specified, while the app is running a test. The results can be viewed on any browser. You can view the results for multiple apps running on different devices, time-synched.

Remote Monitor is available through a monthly subscription service. See our web site for more information about this feature.

Ln Settings

Ln statistical measurements are computed using a 0.10s rate. This speed is selected as it matches most industry-standard sound level meters, and meets the Type 1 ISO/ANSI specifications.

Compute Ln

Turning on this switch causes the Lmax, Lmin, L90, L50, and L10 values to be computed on the current graph. Values are computed for the part of the graph that is currently visible on the screen. These values are also written into the xls file. The values that are in effect at the time that you save the graph are the ones that are stored in the file.

Ln Filter

Select Flat (Z), A, or C weighting. The Ln values will be computed on with the selected filter.

Save 50ms LAeq File

Turning this on causes a file to be saved that includes 50ms LAeq data. This file is named the same as the main file, but has the extension ".text".

Leq/Fast/Slow

Leq means that the Ln values will be computed by an equal-weighted average of each 0.10 second time period.

If Fast or Slow are selected, the appropriate exponential decay detector will be placed before the Ln calculations. You can use this to match test requirements, or to match the operation of an analog sound level meter.

Save Fast 50ms Data File

Available in Octave and 1/3 Octave logging modes, turning this option on will cause another data file to be saved to the public/SPLGraph folder, that contains a list of Fast SPL readings taken every 50ms.

Note that this data cannot be converted to an LAeq, since it uses Fast decay. It may be useful to identify impulsive sound events, and is used by some wind farm community noise specifications.

The file is a normal ASCII unformatted text file, and may be opened in a word processor or Excel or Numbers.

Other Settings

Lock Graph Scale

Turning this switch on prevents any changes from being made to the display graph.

Input Source

This button takes you to the audio input selection screen, where you can choose the input routing (used mostly with iAudioInterface).

dBu Mode

This switch causes the app to work in raw dBu voltage levels, rather than SPL Levels. Use this if you are not working with actual sound levels.

Notifications

Notifications provide a method to get email or iOS notifications upon SPL events. Multiple notifications are supported, and checked after each data point on the graph. So, if your resolution is set to 5 seconds, the notifications will be tested every 5 seconds.

There is a main notifications settings page, and a page for each individual notification.

Main Notifications Settings Page

These settings apply to all notifications.

Email Address and Subject Line Fields

Enter one or two valid email addresses to receive notifications, and a subject line.

Enable Email Switch

Turn this on to enable sending emails.

iOS Notifications Switch

Turn this on to receive iOS and Apple Watch notifications of SPL events.

Lockout Time

After an email is sent, notifications will be locked out and another email will not be sent for this amount of time.

Email Limit

Entering a number here will cause the app to stop sending notifications after this many have been sent. This will reset with each new test run that you start.

Notification List

The table on the right side of the screen shows the list of currently defined notification items. Each notification can be set up differently. Tap a notification to bring up its page.

Add Button

Use the Add button to create a notification.

Notification Page

This page is used to set up or edit a single notification.

Name

Enter the name you wish to assign to this notification.

Type Selector

Select the trigger type, either Leq, or Ln.

Level

Enter the level in dB to test. Note that Ln levels are actually internally tracked as integers, so the value will be rounded to the nearest interger value.

Time

Enter the time in mm:ss that the level must stay at to trigger a notification. For Ln types, as each notification is tested, the test will look back this much time, recompute the Ln over that time interval, and trigger if the Ln value exceeds it.

Time Limits

If desired, enter two 24-hour format times here. Notifications will only be tested between these time limits. Leave these blank to allow testing at any time of day.

Day Of Week Selector

Select the days of the week that you would like to apply to this notification. Days in green will be checked, if the day is red it will be skipped.

SPL Weighting

If you are operating in Octave or 1/3 Octave logging mode, you can choose A/C/Z or any of the octave or 1/3 octave bands to use as the notification trigger.

If you are running on a single filter, that filter is used for computing the notification triggers.

Record Audio

If this is enabled, a clip of the audio that triggered the notification will be recorded and saved locally and to iCloud or Dropbox, if enabled. The clip time will be the same as the Leq / Ln time, up to a maximum time of 30 seconds.

Audio clips are name starting with the letter N, followed by the date and time in ISO format, followed by the notification name. These names will sort by date/time, and you can assign different names to notifications created on different devices, so that the file name will be unique.

Here is an example of a notification name:

N20170724-132658_Notification 1.wav

Email Recorded Audio

Turn this switch on to enable sending the audio clip with the other information in the notification email.

Delete (Trash Can Icon)

Tap this button to delete the notification, after confirming.

Auto Save Setup

Configure the Auto Save Parameters here. Note that we recommend using Dropbox rather than email if possible, please see below. If you are not using the email features, you would just need to set the Auto Save Option switches.

Send To Field

Enter the destination email address here.

Email Settings

Enter your to and from email addresses here.

Auto Save Data at End of Timed Run

Turn this on to enable autosave at the end of a timed run. Note that you must define a stop time for the test on the main SPL Graph settings page.

Email Data on Auto Save

If autosave is enabled, this will cause the data file to be emailed.

Also Save / Email Screen Shot on Auto Save

If enabled, a screen shot will be captured and saved locally (and to any cloud services enabled) as well as emailed.

Restart After Auto Save (Continuous Run)

Enable this option to begin another test after the auto save has occured.

Note that to have continuous data storage, you must define a test stop time, and turn on both "Auto Save Data at End of Timed Run" and "Restart After Save". Emailing data is optional.

Name Options

Tapping this button opens the same auto-save options window that is available from the Save/Recall page, using the mini-menu. It is provided here for convenience.

Send Test Email

Tap this button to send an email to the account defined in the credentials fields above. If you do not get the email, check the your junk mail folder.

Dropbox, iCloud and File Export Options

Dropbox or iCloud support can be enable on the Settings->General screen in the app. The basic data data files, which include the normal XLS tab-delimited files (which have a .txt extension), will be saved automatically to your shared Dropbox or iCloud and will appear moments after the file is saved locally, if you have internet connectivity. If you are not connected to the internet, the files will be copied to your Dropbox or iCloud once you have internet and start the app.

You can optionally store audio files, which may be much larger than the data files, and also the binary internal files, so that you can transfer tests from one iOS device to another. Dropbox does not store video files, but it does store audio files. This is due to a limitation in the Dropbox system.

We recommend using iCloud if possible, since the email server in the app is unable to verify that the files have actually been sent, and so it is possible to miss data.  iCloud is also typically a little quicker than emailing, and allows opening the files from another device that is running the app.