Primer: Using Audacity to estimate average pellet velocity

[bennedose]

What you need:
1. The exact measured distance between muzzle and target
2. A target that makes a loud audible noise when hit by a pellet - like a metal sheet or wooden board.
3. A sound recording device such as a cellphone or laptop (or recording studio if you happen to own one)
4. A computer with audio editing software like Audacity (free) or Adobe Audition (Costs $1arm+1leg)

I suggest that the range from muzzle to target should be more than 10 meters if possible (this is not essential but I will explain below why I say this). Also the recording of sound should be done in an open area relatively free from echoes. Both these suggestions are because the actual sound produced by an air rifle being fired lasts about 0.05 seconds (1/20th second). If there are echoes, or if the target is so close that the pellet hits the target within 1/20th second, you will not be able to make out the point where the sound of the target being hit is heard because that sound will be covered up by the sound of the rifle itself. The sound of rifle/pistol going off and target being hit will simply blend into one continuous sound which is then not useful for any estimation.

Before you start recording remember to speak into the mike and say what rifle/pistol, what pellet and what range because you will forget to do that and won't know what the recording might be.

It is best to put the sound recording device approximately mid-way between the muzzle and the target. When you do that the time taken for the sound to reach the mike from the muzzle and from the target is the same so that errors due to the time taken for sound to travel are eliminated. Even otherwise the difference is small, but at higher ranges the calculation gets affected.

Here is a recording of a target being hit by two pellets using an IHP 35 at 16 meters. There is no need to listen to the sound, but if you want to play with the file you can download it.
https://docs.google.com/file/d/0B3JNY4I ... sp=sharing

I fired up Audacity sound editing softwware and opened the above file in it. The following image is the sound wave recording that I got. I have labelled events like cocking of rifle, closing of breech and the sound of the rifle being shot and the pellet hitting the target. Note that the gap between shooting and hitiing target is very small.If the gap had been smaller it would have been impossible to separate the sounds of shooting and hitting.
https://docs.google.com/file/d/0B3JNY4I ... sp=sharing

In the following image I have edited out and deleted unnecsssary parts like sound of cocking and closing and tin can falling. (Select the unnecessary parts with mouse and hit delete). This leaves only the enlarged sound picture of rifle shot and pellet hitting target. You can expand or contract the sound graph/image vertically and horizontally to enlarge it or make it smaller as required using the "View" menu. The following is an enlarged view of the same pellet sounds visible in the previous image. Here you can clearly see the separation between the two sounds - of shot being fired and pellet hitting target because of the horizontal enlargement.

Use the mouse to select precisely from the start of the rifle shot sound to the start of the pellet hitting sound (Use left click and drag). Once that is selected the timelength of the selected part is displayed below. In my image the time length is 0.104 seconds (about 1/10th second)
https://docs.google.com/file/d/0B3JNY4I ... sp=sharing

Now we have the distance (or range) - 16 meters as measured earlier
Time of travel of pellet is 0.104 seconds
Speed= Distance/Time= 16/0.104
= 154 meters per sec (or about 500 fps)

NOTE: Audacity has a function that enables it to automatically recognize two sounds like shot and pellet hitting. That function requires some adjusments and settings that I hate doing. The results are rarely any different from what I get if I select the sounds manually so I never use the "detect sound" function. But you can try it if you like

[Basu]

Dear benne,
I request you to compare the velocity given by Audacity with
cronoconnect datas side by side.

Basu

[bennedose]

Basu, I have done that. Chrono conect velocities are higher and understandably so because Chrono computes muzzle velocity and Audacity only looks at average velocity. If I do the same test with the same pellet at lower ranges the velocity will be higher with Audacity.

In fact I have a couple of "experiments" in mind which I might do when the weather improved. I want to generate a graph of Audacity values at 5, 10, 15 and 20 meters and I expect a curve that can be extrapolated backwards to zero meters to calculate muzzle velocity. Just time-pass

[bennedose]

Dear benne,
I request you to compare the velocity given by Audacity with
cronoconnect datas side by side.

Basu

I repeated these tests in the last 2 days using 1 gram Mastershot Wadcutter and 700 mg AIMCO round head and my SDB

At 15 meter range Audacity gives the following average velocity
MS Wadcutter: 100 meters per sec
AIMCO round: 110 meters per sec

At 15 meters Chrono connect lite gives the following muzzle velocties
MS Wadcutter : 130 meters per sec
AIMCO: 144 to 150 meters per sec

The Audacity values and Chrono values are moderately consistent at 15 meters. Naturally muzzle velocity is the fastest while average velocity will be lower

But at 10 meters range the values I got were all off the mark. I got lower velocities both in Audacity and Chrono connect. It seems that the sound picture at 10 meters or less in my backyard range is affected by echoes and other inaccuracies and the shorter range values are erroneous - with both Audacity and Chrono connect. Pellets are showing higher velocities at longer ranges and lower velocities at short range. This cannot be right. A pellet cannot speed up in the air. If my pellets are doing that they are rockets, not pellets

[brihacharan]

Dear benne,
I request you to compare the velocity given by Audacity with chrono-connect data side by side.

Basu

I repeated these tests in the last 2 days using 1 gram Mastershot Wadcutter and 700 mg AIMCO round head and my SDB

At 15 meter range Audacity gives the following average velocity
MS Wadcutter: 100 meters per sec = 360fps
AIMCO round: 110 meters per sec = 396fps

At 15 meters Chrono connect lite gives the following muzzle velocties
MS Wadcutter : 130 meters per sec = 365fps
AIMCO: 144 to 150 meters per sec = 495fps

The Audacity values and Chrono values are moderately consistent at 15 meters. Naturally muzzle velocity is the fastest while average velocity will be lower

But at 10 meters range the values I got were all off the mark. I got lower velocities both in Audacity and Chrono connect. It seems that the sound picture at 10 meters or less in my backyard range is affected by echoes and other inaccuracies and the shorter range values are erroneous - with both Audacity and Chrono connect. Pellets are showing higher velocities at longer ranges and lower velocities at short range. This cannot be right. A pellet cannot speed up in the air. If my pellets are doing that they are rockets, not pellets

Bennedose,
Great experiments
However Chrono values seem to be more realistic!
The velocities at longer & shorter ranges as mentioned above totally beats the laws of physics
My humble conclusion is that - Assessing velocities by Computer aided programs are at best 'indicative' and not realistic & conclusive
What's your take?
Briha

[bennedose]

My humble conclusion is that - Assessing velocities by Computer aided programs are at best 'indicative' and not realistic & conclusive
What's your take?
Briha

Oh absolutely. Although I actually went through the trouble of using both Audacity and Chrono at 10 meters also I deliberately did not post the results here because they looked so stupid.

With Chrono I got 90 m/sec at 10 meters and 110 meters per sec at 15 meters. This would suggest that my pellets are leaving the rifle and then somehow accelerating themselves

With Audacity, using wadcutters I got 100 m/sec at 5, 10 and 15 and 18 meters. No slowing down whatsoever from air resistance at longer ranges

Either:
1. My pellets are accelerating by themselves after leaving the rifle
or
2. I did the tests on the moon with zero air resistance
or
3. The test methods are not particularly accurate or dependable and as you say:

Assessing velocities by Computer aided programs are at best 'indicative' and not realistic & conclusive

[Basu]

I have no clue whatsoever ,as to why results are so ridiculous.
I have tested Audacity figures and cronoconnect at a fixed distance of 9-10 mts with Gsmith ameteur.177.
Muzzle velocity audacity- 686 fps
cronoconnect - 710 fps.
In National 25
audacity muzzle -548 fps
cronoconnect - 565 fps
The muzzle velocity in audacity is derived by deviding average velocity with .965 as suggested by Harshabardhan.
Cronoconnect himself has suggested that best result is obtained at 10 mts.
There is another sound soft crono available at talonairgun.Though I downloaded but it does not open in my computer.Harsha suggest he gets quite consistant results with that.

Basu

[bennedose]

Basu I have some idea why the results are on the low side - apart from being 0.22 pellets.

My SDB 50 had a replacement Cherokee spring that was too powerful and all it was doing was causing dieseling and was very inaccurate after re springing and I was very unhappy. So I opened up the rifle and arbitrarily cut off 1.5 inches of spring. After that the power was very much reduced but shooting has been smooth accurate and a real pleasure.

When I use light (11 grain-700 mg) AIMCO or Marshal shot flat head pellets I get a consistent 150 meters per sec or about 525 fps as indicated by the Chrono connect meaurements. Part of the problem is surely the fact that my backyard shooting range has walls on 2 sides and acts like an echo chamber.